Fix TabBar initialization issue and add tests

scene/gui/tab_bar.cpp

@@ -354,6 +354,8 @@ void TabBar::_notification(int p_what) {
 			if (scroll_to_selected) {
 				ensure_tab_visible(current);
 			}
+			// Set initialized even if no tabs were set.
+			initialized = true;
 		} break;
 
 		case NOTIFICATION_INTERNAL_PROCESS: {
@@ -655,10 +657,10 @@ void TabBar::set_tab_count(int p_count) {
 	}
 
 	if (!initialized) {
-		if (queued_current != current) {
-			current = queued_current;
-		}
 		initialized = true;
+		if (queued_current != CURRENT_TAB_UNINITIALIZED && queued_current != current) {
+			set_current_tab(queued_current);
+		}
 	}
 
 	queue_redraw();
@@ -740,6 +742,13 @@ bool TabBar::select_next_available() {
 	return false;
 }
 
+void TabBar::set_tab_offset(int p_offset) {
+	ERR_FAIL_INDEX(p_offset, tabs.size());
+	offset = p_offset;
+	_update_cache();
+	queue_redraw();
+}
+
 int TabBar::get_tab_offset() const {
 	return offset;
 }

scene/gui/tab_bar.h

@@ -117,8 +117,9 @@ private:
 	bool scroll_to_selected = true;
 	int tabs_rearrange_group = -1;
 
+	static const int CURRENT_TAB_UNINITIALIZED = -2;
 	bool initialized = false;
-	int queued_current = -1;
+	int queued_current = CURRENT_TAB_UNINITIALIZED;
 
 	const float DEFAULT_GAMEPAD_EVENT_DELAY_MS = 0.5;
 	const float GAMEPAD_EVENT_REPEAT_RATE_MS = 1.0 / 20;
@@ -249,6 +250,7 @@ public:
 	bool select_previous_available();
 	bool select_next_available();
 
+	void set_tab_offset(int p_offset);
 	int get_tab_offset() const;
 	bool get_offset_buttons_visible() const;
 

scene/gui/tab_container.cpp

@@ -190,7 +190,7 @@ void TabContainer::_notification(int p_what) {
 		} break;
 
 		case NOTIFICATION_VISIBILITY_CHANGED: {
-			if (!is_visible() || setup_current_tab > -2) {
+			if (!is_visible()) {
 				return;
 			}
 
@@ -200,7 +200,7 @@ void TabContainer::_notification(int p_what) {
 			// beat it to the punch and make sure that the correct node is the only one visible first.
 			// Otherwise, it can prevent a tab change done right before this container was made visible.
 			Vector<Control *> controls = _get_tab_controls();
-			int current = get_current_tab();
+			int current = setup_current_tab > -2 ? setup_current_tab : get_current_tab();
 			for (int i = 0; i < controls.size(); i++) {
 				controls[i]->set_visible(i == current);
 			}

tests/scene/test_tab_bar.h

@@ -0,0 +1,864 @@
+/**************************************************************************/
+/*  test_tab_bar.h                                                        */
+/**************************************************************************/
+/*                         This file is part of:                          */
+/*                             GODOT ENGINE                               */
+/*                        https://godotengine.org                         */
+/**************************************************************************/
+/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
+/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur.                  */
+/*                                                                        */
+/* Permission is hereby granted, free of charge, to any person obtaining  */
+/* a copy of this software and associated documentation files (the        */
+/* "Software"), to deal in the Software without restriction, including    */
+/* without limitation the rights to use, copy, modify, merge, publish,    */
+/* distribute, sublicense, and/or sell copies of the Software, and to     */
+/* permit persons to whom the Software is furnished to do so, subject to  */
+/* the following conditions:                                              */
+/*                                                                        */
+/* The above copyright notice and this permission notice shall be         */
+/* included in all copies or substantial portions of the Software.        */
+/*                                                                        */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,        */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF     */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. */
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY   */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,   */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE      */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                 */
+/**************************************************************************/
+
+#ifndef TEST_TAB_BAR_H
+#define TEST_TAB_BAR_H
+
+#include "scene/gui/tab_bar.h"
+#include "scene/main/window.h"
+
+#include "tests/test_macros.h"
+
+namespace TestTabBar {
+static inline Array build_array() {
+	return Array();
+}
+template <typename... Targs>
+static inline Array build_array(Variant item, Targs... Fargs) {
+	Array a = build_array(Fargs...);
+	a.push_front(item);
+	return a;
+}
+
+TEST_CASE("[SceneTree][TabBar] tab operations") {
+	TabBar *tab_bar = memnew(TabBar);
+	SceneTree::get_singleton()->get_root()->add_child(tab_bar);
+	tab_bar->set_clip_tabs(false);
+	MessageQueue::get_singleton()->flush();
+
+	SIGNAL_WATCH(tab_bar, "tab_selected");
+	SIGNAL_WATCH(tab_bar, "tab_changed");
+
+	SUBCASE("[TabBar] no tabs") {
+		CHECK(tab_bar->get_tab_count() == 0);
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == -1);
+	}
+
+	SUBCASE("[TabBar] add tabs") {
+		tab_bar->add_tab("tab0");
+		CHECK(tab_bar->get_tab_count() == 1);
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(0)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(0)));
+
+		tab_bar->add_tab("tab1");
+		CHECK(tab_bar->get_tab_count() == 2);
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		tab_bar->add_tab("tab2");
+		CHECK(tab_bar->get_tab_count() == 3);
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		CHECK(tab_bar->get_tab_title(0) == "tab0");
+		CHECK(tab_bar->get_tab_tooltip(0) == "");
+		CHECK(tab_bar->get_tab_text_direction(0) == Control::TEXT_DIRECTION_INHERITED);
+		CHECK_FALSE(tab_bar->is_tab_disabled(0));
+		CHECK_FALSE(tab_bar->is_tab_hidden(0));
+
+		CHECK(tab_bar->get_tab_title(1) == "tab1");
+		CHECK(tab_bar->get_tab_tooltip(1) == "");
+		CHECK(tab_bar->get_tab_text_direction(1) == Control::TEXT_DIRECTION_INHERITED);
+		CHECK_FALSE(tab_bar->is_tab_disabled(1));
+		CHECK_FALSE(tab_bar->is_tab_hidden(1));
+
+		CHECK(tab_bar->get_tab_title(2) == "tab2");
+		CHECK(tab_bar->get_tab_tooltip(2) == "");
+		CHECK(tab_bar->get_tab_text_direction(2) == Control::TEXT_DIRECTION_INHERITED);
+		CHECK_FALSE(tab_bar->is_tab_disabled(2));
+		CHECK_FALSE(tab_bar->is_tab_hidden(2));
+	}
+
+	SUBCASE("[TabBar] set tab count") {
+		// Adds multiple tabs at once.
+		tab_bar->set_tab_count(3);
+		CHECK(tab_bar->get_tab_count() == 3);
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		CHECK(tab_bar->get_tab_title(0) == "");
+		CHECK(tab_bar->get_tab_tooltip(0) == "");
+		CHECK(tab_bar->get_tab_text_direction(0) == Control::TEXT_DIRECTION_INHERITED);
+		CHECK_FALSE(tab_bar->is_tab_disabled(0));
+		CHECK_FALSE(tab_bar->is_tab_hidden(0));
+
+		CHECK(tab_bar->get_tab_title(1) == "");
+		CHECK(tab_bar->get_tab_tooltip(1) == "");
+		CHECK(tab_bar->get_tab_text_direction(1) == Control::TEXT_DIRECTION_INHERITED);
+		CHECK_FALSE(tab_bar->is_tab_disabled(1));
+		CHECK_FALSE(tab_bar->is_tab_hidden(1));
+
+		CHECK(tab_bar->get_tab_title(2) == "");
+		CHECK(tab_bar->get_tab_tooltip(2) == "");
+		CHECK(tab_bar->get_tab_text_direction(2) == Control::TEXT_DIRECTION_INHERITED);
+		CHECK_FALSE(tab_bar->is_tab_disabled(2));
+		CHECK_FALSE(tab_bar->is_tab_hidden(2));
+
+		// Setting to less tabs than there are removes from the end.
+		tab_bar->set_tab_title(0, "tab0");
+		tab_bar->set_tab_title(1, "tab1");
+		tab_bar->set_tab_title(2, "tab2");
+
+		tab_bar->set_tab_count(2);
+		CHECK(tab_bar->get_tab_count() == 2);
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		CHECK(tab_bar->get_tab_title(0) == "tab0");
+		CHECK(tab_bar->get_tab_title(1) == "tab1");
+
+		// Remove all tabs.
+		tab_bar->set_tab_count(0);
+		CHECK(tab_bar->get_tab_count() == 0);
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == -1);
+	}
+
+	SUBCASE("[TabBar] clear tabs") {
+		CHECK(tab_bar->get_tab_count() == 0);
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == -1);
+
+		tab_bar->set_tab_count(2);
+		CHECK(tab_bar->get_tab_count() == 2);
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		tab_bar->clear_tabs();
+		CHECK(tab_bar->get_tab_count() == 0);
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+	}
+
+	SUBCASE("[TabBar] remove tabs") {
+		tab_bar->add_tab("tab0");
+		tab_bar->add_tab("tab1");
+		tab_bar->add_tab("tab2");
+		tab_bar->set_current_tab(1);
+		CHECK(tab_bar->get_tab_count() == 3);
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		// Remove first tab.
+		tab_bar->remove_tab(0);
+		CHECK(tab_bar->get_tab_count() == 2);
+		CHECK(tab_bar->get_tab_title(0) == "tab1");
+		CHECK(tab_bar->get_tab_title(1) == "tab2");
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Remove last tab.
+		tab_bar->remove_tab(1);
+		CHECK(tab_bar->get_tab_count() == 1);
+		CHECK(tab_bar->get_tab_title(0) == "tab1");
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Remove only tab.
+		tab_bar->remove_tab(0);
+		CHECK(tab_bar->get_tab_count() == 0);
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK("tab_changed", build_array(build_array(-1)));
+
+		// Remove current tab when there are other tabs.
+		tab_bar->add_tab("tab0");
+		tab_bar->add_tab("tab1");
+		tab_bar->add_tab("tab2");
+		tab_bar->set_current_tab(1);
+		tab_bar->set_current_tab(2);
+		CHECK(tab_bar->get_tab_count() == 3);
+		CHECK(tab_bar->get_current_tab() == 2);
+		CHECK(tab_bar->get_previous_tab() == 1);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		tab_bar->remove_tab(2);
+		CHECK(tab_bar->get_tab_count() == 2);
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK("tab_changed", build_array(build_array(1)));
+	}
+
+	SUBCASE("[TabBar] move tabs") {
+		tab_bar->add_tab("tab0");
+		tab_bar->add_tab("tab1");
+		tab_bar->add_tab("tab2");
+		tab_bar->set_current_tab(1);
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		// Don't move if index is the same.
+		tab_bar->move_tab(0, 0);
+		CHECK(tab_bar->get_tab_title(0) == "tab0");
+		CHECK(tab_bar->get_tab_title(1) == "tab1");
+		CHECK(tab_bar->get_tab_title(2) == "tab2");
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Move the first tab to the end.
+		tab_bar->move_tab(0, 2);
+		CHECK(tab_bar->get_tab_title(0) == "tab1");
+		CHECK(tab_bar->get_tab_title(1) == "tab2");
+		CHECK(tab_bar->get_tab_title(2) == "tab0");
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == 2);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Move the second tab to the front.
+		tab_bar->move_tab(1, 0);
+		CHECK(tab_bar->get_tab_title(0) == "tab2");
+		CHECK(tab_bar->get_tab_title(1) == "tab1");
+		CHECK(tab_bar->get_tab_title(2) == "tab0");
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 2);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+	}
+
+	SUBCASE("[TabBar] set current tab") {
+		tab_bar->add_tab("tab0");
+		tab_bar->add_tab("tab1");
+		tab_bar->add_tab("tab2");
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(0)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(0)));
+
+		// Set the current tab.
+		tab_bar->set_current_tab(1);
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(1)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(1)));
+
+		// Set to same tab.
+		tab_bar->set_current_tab(1);
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 1);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(1)));
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Out of bounds.
+		ERR_PRINT_OFF;
+		tab_bar->set_current_tab(-5);
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		tab_bar->set_current_tab(5);
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+		ERR_PRINT_ON;
+	}
+
+	SUBCASE("[TabBar] deselection enabled") {
+		tab_bar->add_tab("tab0");
+		tab_bar->add_tab("tab1");
+		tab_bar->add_tab("tab2");
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		// Setting deselect enabled doesn't change current tab.
+		tab_bar->set_deselect_enabled(true);
+		CHECK(tab_bar->get_deselect_enabled());
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Can deselect all tabs by setting current to -1.
+		tab_bar->set_current_tab(-1);
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(-1)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(-1)));
+
+		// Adding a tab will still set the current tab to 0.
+		tab_bar->clear_tabs();
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == -1);
+
+		tab_bar->add_tab("tab0");
+		tab_bar->add_tab("tab1");
+		tab_bar->add_tab("tab2");
+		CHECK(tab_bar->get_tab_count() == 3);
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(0)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(0)));
+
+		tab_bar->set_current_tab(-1);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		// Disabling while at -1 will select the first available tab.
+		tab_bar->set_deselect_enabled(false);
+		CHECK_FALSE(tab_bar->get_deselect_enabled());
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(0)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(0)));
+
+		// Cannot set to -1 if disabled.
+		ERR_PRINT_OFF;
+		tab_bar->set_current_tab(-1);
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+		ERR_PRINT_ON;
+
+		// Disabling while at -1 skips any disabled or hidden tabs.
+		tab_bar->set_deselect_enabled(true);
+		tab_bar->set_tab_disabled(0, true);
+		tab_bar->set_tab_hidden(1, true);
+		tab_bar->set_current_tab(-1);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+		tab_bar->set_deselect_enabled(false);
+		CHECK(tab_bar->get_current_tab() == 2);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(2)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(2)));
+	}
+
+	SUBCASE("[TabBar] hidden tabs") {
+		tab_bar->add_tab("tab0");
+		tab_bar->add_tab("tab1");
+		tab_bar->add_tab("tab2");
+		tab_bar->set_current_tab(1);
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		CHECK_FALSE(tab_bar->is_tab_hidden(1));
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		MessageQueue::get_singleton()->flush();
+		Vector<Rect2> tab_rects = {
+			tab_bar->get_tab_rect(0),
+			tab_bar->get_tab_rect(1),
+			tab_bar->get_tab_rect(2)
+		};
+
+		// Hiding a tab does not affect current tab.
+		tab_bar->set_tab_hidden(1, true);
+		CHECK(tab_bar->is_tab_hidden(1));
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// The tabs after are moved over.
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab_bar->get_tab_rect(0) == tab_rects[0]);
+		CHECK(tab_bar->get_tab_rect(2) == tab_rects[1]);
+
+		// Unhiding a tab does not affect current tab.
+		tab_bar->set_tab_hidden(1, false);
+		CHECK_FALSE(tab_bar->is_tab_hidden(1));
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// The tabs are back where they were.
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab_bar->get_tab_rect(0) == tab_rects[0]);
+		CHECK(tab_bar->get_tab_rect(1) == tab_rects[1]);
+		CHECK(tab_bar->get_tab_rect(2) == tab_rects[2]);
+	}
+
+	SUBCASE("[TabBar] disabled tabs") {
+		tab_bar->add_tab("tab0");
+		tab_bar->add_tab("tab1");
+		tab_bar->add_tab("tab2");
+		CHECK_FALSE(tab_bar->is_tab_disabled(1));
+		tab_bar->set_current_tab(1);
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		CHECK_FALSE(tab_bar->is_tab_hidden(1));
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		// Disabling a tab does not affect current tab.
+		tab_bar->set_tab_disabled(1, true);
+		CHECK(tab_bar->is_tab_disabled(1));
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Enabling a tab does not affect current tab.
+		tab_bar->set_tab_disabled(1, false);
+		CHECK_FALSE(tab_bar->is_tab_disabled(1));
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+	}
+
+	SUBCASE("[TabBar] select next available") {
+		tab_bar->add_tab("tab0");
+		tab_bar->add_tab("tab1");
+		tab_bar->add_tab("tab2");
+		tab_bar->add_tab("tab3");
+		tab_bar->add_tab("tab4");
+		tab_bar->set_tab_disabled(2, true);
+		tab_bar->set_tab_hidden(3, true);
+		tab_bar->set_current_tab(0);
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		// Selects the next tab.
+		CHECK(tab_bar->select_next_available());
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(1)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(1)));
+
+		// Skips over disabled and hidden tabs.
+		CHECK(tab_bar->select_next_available());
+		CHECK(tab_bar->get_current_tab() == 4);
+		CHECK(tab_bar->get_previous_tab() == 1);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(4)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(4)));
+
+		// Does not wrap around.
+		CHECK_FALSE(tab_bar->select_next_available());
+		CHECK(tab_bar->get_current_tab() == 4);
+		CHECK(tab_bar->get_previous_tab() == 1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Fails if there is only one valid tab.
+		tab_bar->remove_tab(0);
+		tab_bar->remove_tab(3);
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		CHECK_FALSE(tab_bar->select_next_available());
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Fails if there are no valid tabs.
+		tab_bar->remove_tab(0);
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		CHECK_FALSE(tab_bar->select_next_available());
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Fails if there are no tabs.
+		tab_bar->clear_tabs();
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		CHECK_FALSE(tab_bar->select_next_available());
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+	}
+
+	SUBCASE("[TabBar] select previous available") {
+		tab_bar->add_tab("tab0");
+		tab_bar->add_tab("tab1");
+		tab_bar->add_tab("tab2");
+		tab_bar->add_tab("tab3");
+		tab_bar->add_tab("tab4");
+		tab_bar->set_tab_disabled(1, true);
+		tab_bar->set_tab_hidden(2, true);
+		tab_bar->set_current_tab(4);
+		CHECK(tab_bar->get_current_tab() == 4);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		// Selects the previous tab.
+		CHECK(tab_bar->select_previous_available());
+		CHECK(tab_bar->get_current_tab() == 3);
+		CHECK(tab_bar->get_previous_tab() == 4);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(3)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(3)));
+
+		// Skips over disabled and hidden tabs.
+		CHECK(tab_bar->select_previous_available());
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == 3);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(0)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(0)));
+
+		// Does not wrap around.
+		CHECK_FALSE(tab_bar->select_previous_available());
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == 3);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Fails if there is only one valid tab.
+		tab_bar->remove_tab(4);
+		tab_bar->remove_tab(3);
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == 2);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		CHECK_FALSE(tab_bar->select_previous_available());
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == 2);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Fails if there are no valid tabs.
+		tab_bar->remove_tab(0);
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == 1);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		CHECK_FALSE(tab_bar->select_previous_available());
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == 1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Fails if there are no tabs.
+		tab_bar->clear_tabs();
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		CHECK_FALSE(tab_bar->select_previous_available());
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+	}
+
+	SIGNAL_UNWATCH(tab_bar, "tab_selected");
+	SIGNAL_UNWATCH(tab_bar, "tab_changed");
+
+	memdelete(tab_bar);
+}
+
+TEST_CASE("[SceneTree][TabBar] initialization") {
+	TabBar *tab_bar = memnew(TabBar);
+
+	SIGNAL_WATCH(tab_bar, "tab_selected");
+	SIGNAL_WATCH(tab_bar, "tab_changed");
+
+	SUBCASE("[TabBar] current tab can be set before tabs are set") {
+		// This queues the current tab to update on when tabs are set.
+		tab_bar->set_current_tab(1);
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		tab_bar->set_tab_count(2);
+		CHECK(tab_bar->get_tab_count() == 2);
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(1)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(1)));
+
+		// Does not work again.
+		ERR_PRINT_OFF;
+		tab_bar->set_current_tab(2);
+		CHECK(tab_bar->get_tab_count() == 2);
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		tab_bar->set_tab_count(3);
+		CHECK(tab_bar->get_tab_count() == 3);
+		CHECK(tab_bar->get_current_tab() == 1);
+		CHECK(tab_bar->get_previous_tab() == 0);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+		ERR_PRINT_ON;
+	}
+
+	SUBCASE("[TabBar] setting tabs works normally if no current tab was set") {
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == -1);
+
+		tab_bar->set_tab_count(2);
+		CHECK(tab_bar->get_tab_count() == 2);
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+	}
+
+	SUBCASE("[TabBar] cannot set current tab to an invalid value before tabs are set") {
+		tab_bar->set_current_tab(100);
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// This will print an error message as if `set_current_tab` was called after.
+		ERR_PRINT_OFF;
+		tab_bar->set_tab_count(2);
+		CHECK(tab_bar->get_tab_count() == 2);
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+		ERR_PRINT_ON;
+	}
+
+	SUBCASE("[TabBar] setting the current tab before tabs only works when out of tree") {
+		tab_bar->set_current_tab(1);
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		SceneTree::get_singleton()->get_root()->add_child(tab_bar);
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab_bar->get_tab_count() == 0);
+		CHECK(tab_bar->get_current_tab() == -1);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Works normally.
+		tab_bar->set_tab_count(2);
+		CHECK(tab_bar->get_tab_count() == 2);
+		CHECK(tab_bar->get_current_tab() == 0);
+		CHECK(tab_bar->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+	}
+
+	SIGNAL_UNWATCH(tab_bar, "tab_selected");
+	SIGNAL_UNWATCH(tab_bar, "tab_changed");
+
+	memdelete(tab_bar);
+}
+
+TEST_CASE("[SceneTree][TabBar] layout and offset") {
+	TabBar *tab_bar = memnew(TabBar);
+	SceneTree::get_singleton()->get_root()->add_child(tab_bar);
+
+	tab_bar->set_clip_tabs(false);
+	tab_bar->add_tab("tab0");
+	tab_bar->add_tab("tab1 ");
+	tab_bar->add_tab("tab2    ");
+	MessageQueue::get_singleton()->flush();
+	Size2 all_tabs_size = tab_bar->get_size();
+
+	Vector<Rect2> tab_rects = {
+		tab_bar->get_tab_rect(0),
+		tab_bar->get_tab_rect(1),
+		tab_bar->get_tab_rect(2)
+	};
+
+	SUBCASE("[TabBar] tabs are arranged next to each other") {
+		// Horizontal positions are next to each other.
+		CHECK(tab_rects[0].position.x == 0);
+		CHECK(tab_rects[1].position.x == tab_rects[0].size.x);
+		CHECK(tab_rects[2].position.x == tab_rects[1].position.x + tab_rects[1].size.x);
+
+		// Fills the entire width.
+		CHECK(tab_rects[2].position.x + tab_rects[2].size.x == all_tabs_size.x);
+
+		// Horizontal sizes are positive.
+		CHECK(tab_rects[0].size.x > 0);
+		CHECK(tab_rects[1].size.x > 0);
+		CHECK(tab_rects[2].size.x > 0);
+
+		// Vertical positions are at 0.
+		CHECK(tab_rects[0].position.y == 0);
+		CHECK(tab_rects[1].position.y == 0);
+		CHECK(tab_rects[2].position.y == 0);
+
+		// Vertical sizes are the same.
+		CHECK(tab_rects[0].size.y == tab_rects[1].size.y);
+		CHECK(tab_rects[1].size.y == tab_rects[2].size.y);
+	}
+
+	SUBCASE("[TabBar] tab alignment") {
+		// Add extra space so the alignment can be seen.
+		tab_bar->set_size(Size2(all_tabs_size.x + 100, all_tabs_size.y));
+
+		// Left alignment.
+		tab_bar->set_tab_alignment(TabBar::ALIGNMENT_LEFT);
+		MessageQueue::get_singleton()->flush();
+		tab_rects = {
+			tab_bar->get_tab_rect(0),
+			tab_bar->get_tab_rect(1),
+			tab_bar->get_tab_rect(2)
+		};
+		CHECK(tab_bar->get_tab_alignment() == TabBar::ALIGNMENT_LEFT);
+		CHECK(tab_rects[0].position.x == 0);
+		CHECK(tab_rects[1].position.x == tab_rects[0].size.x);
+		CHECK(tab_rects[2].position.x == tab_rects[1].position.x + tab_rects[1].size.x);
+
+		// Right alignment.
+		tab_bar->set_tab_alignment(TabBar::ALIGNMENT_RIGHT);
+		MessageQueue::get_singleton()->flush();
+		tab_rects = {
+			tab_bar->get_tab_rect(0),
+			tab_bar->get_tab_rect(1),
+			tab_bar->get_tab_rect(2)
+		};
+		CHECK(tab_bar->get_tab_alignment() == TabBar::ALIGNMENT_RIGHT);
+		CHECK(tab_rects[2].position.x == tab_bar->get_size().x - tab_rects[2].size.x);
+		CHECK(tab_rects[1].position.x == tab_rects[2].position.x - tab_rects[1].size.x);
+		CHECK(tab_rects[0].position.x == tab_rects[1].position.x - tab_rects[0].size.x);
+
+		// Center alignment.
+		tab_bar->set_tab_alignment(TabBar::ALIGNMENT_CENTER);
+		MessageQueue::get_singleton()->flush();
+		tab_rects = {
+			tab_bar->get_tab_rect(0),
+			tab_bar->get_tab_rect(1),
+			tab_bar->get_tab_rect(2)
+		};
+		CHECK(tab_bar->get_tab_alignment() == TabBar::ALIGNMENT_CENTER);
+		float center_pos = tab_bar->get_size().x / 2;
+		CHECK(tab_rects[0].position.x == center_pos - all_tabs_size.x / 2);
+		CHECK(tab_rects[1].position.x == tab_rects[0].position.x + tab_rects[0].size.x);
+		CHECK(tab_rects[2].position.x == tab_rects[1].position.x + tab_rects[1].size.x);
+	}
+
+	SUBCASE("[TabBar] clip tabs") {
+		// Clip tabs disabled means all tabs are visible and the minimum size holds all of them.
+		tab_bar->set_clip_tabs(false);
+		CHECK_FALSE(tab_bar->get_clip_tabs());
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab_bar->get_tab_offset() == 0);
+		CHECK(tab_bar->get_minimum_size() == tab_bar->get_size());
+		CHECK(tab_bar->get_size().x == tab_rects[0].size.x + tab_rects[1].size.x + tab_rects[2].size.x);
+		CHECK(tab_bar->get_size().y == MAX(tab_rects[0].size.y, MAX(tab_rects[1].size.y, tab_rects[2].size.y)));
+
+		tab_bar->set_clip_tabs(true);
+		CHECK(tab_bar->get_clip_tabs());
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab_bar->get_tab_offset() == 0);
+
+		// Horizontal size and minimum size get set to 0.
+		CHECK(tab_bar->get_minimum_size().x == 0);
+		CHECK(tab_bar->get_minimum_size().y == all_tabs_size.y);
+		CHECK(tab_bar->get_size().x == 0);
+		CHECK(tab_bar->get_size().y == all_tabs_size.y);
+	}
+
+	SUBCASE("[TabBar] ensure tab visible") {
+		tab_bar->set_scroll_to_selected(false);
+		tab_bar->set_clip_tabs(true);
+
+		// Resize tab bar to only be able to fit 2 tabs.
+		const float offset_button_size = tab_bar->get_theme_icon("decrement_icon")->get_width() + tab_bar->get_theme_icon("increment_icon")->get_width();
+		tab_bar->set_size(Size2(tab_rects[2].size.x + tab_rects[1].size.x + offset_button_size, all_tabs_size.y));
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab_bar->get_tab_offset() == 0);
+		CHECK(tab_bar->get_offset_buttons_visible());
+
+		// Scroll right to a tab that is not visible.
+		tab_bar->ensure_tab_visible(2);
+		CHECK(tab_bar->get_tab_offset() == 1);
+		CHECK(tab_bar->get_tab_rect(1).position.x == 0);
+		CHECK(tab_bar->get_tab_rect(2).position.x == tab_rects[1].size.x);
+
+		tab_bar->set_tab_offset(2);
+		CHECK(tab_bar->get_tab_offset() == 2);
+		CHECK(tab_bar->get_tab_rect(2).position.x == 0);
+
+		// Scroll left to a previous tab.
+		tab_bar->ensure_tab_visible(1);
+		CHECK(tab_bar->get_tab_offset() == 1);
+		CHECK(tab_bar->get_tab_rect(1).position.x == 0);
+		CHECK(tab_bar->get_tab_rect(2).position.x == tab_rects[1].size.x);
+
+		// Will not scroll if the tab is already visible.
+		tab_bar->ensure_tab_visible(2);
+		CHECK(tab_bar->get_tab_offset() == 1);
+		CHECK(tab_bar->get_tab_rect(1).position.x == 0);
+		CHECK(tab_bar->get_tab_rect(2).position.x == tab_rects[1].size.x);
+	}
+
+	memdelete(tab_bar);
+}
+
+// FIXME: Add tests for mouse click, keyboard navigation, and drag and drop.
+
+} // namespace TestTabBar
+
+#endif // TEST_TAB_BAR_H

tests/scene/test_tab_container.h

@@ -0,0 +1,671 @@
+/**************************************************************************/
+/*  test_tab_container.h                                                  */
+/**************************************************************************/
+/*                         This file is part of:                          */
+/*                             GODOT ENGINE                               */
+/*                        https://godotengine.org                         */
+/**************************************************************************/
+/* Copyright (c) 2014-present Godot Engine contributors (see AUTHORS.md). */
+/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur.                  */
+/*                                                                        */
+/* Permission is hereby granted, free of charge, to any person obtaining  */
+/* a copy of this software and associated documentation files (the        */
+/* "Software"), to deal in the Software without restriction, including    */
+/* without limitation the rights to use, copy, modify, merge, publish,    */
+/* distribute, sublicense, and/or sell copies of the Software, and to     */
+/* permit persons to whom the Software is furnished to do so, subject to  */
+/* the following conditions:                                              */
+/*                                                                        */
+/* The above copyright notice and this permission notice shall be         */
+/* included in all copies or substantial portions of the Software.        */
+/*                                                                        */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,        */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF     */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. */
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY   */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,   */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE      */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                 */
+/**************************************************************************/
+
+#ifndef TEST_TAB_CONTAINER_H
+#define TEST_TAB_CONTAINER_H
+
+#include "scene/gui/tab_container.h"
+
+#include "tests/test_macros.h"
+
+namespace TestTabContainer {
+static inline Array build_array() {
+	return Array();
+}
+template <typename... Targs>
+static inline Array build_array(Variant item, Targs... Fargs) {
+	Array a = build_array(Fargs...);
+	a.push_front(item);
+	return a;
+}
+
+TEST_CASE("[SceneTree][TabContainer] tab operations") {
+	TabContainer *tab_container = memnew(TabContainer);
+	SceneTree::get_singleton()->get_root()->add_child(tab_container);
+	MessageQueue::get_singleton()->flush();
+	SIGNAL_WATCH(tab_container, "tab_selected");
+	SIGNAL_WATCH(tab_container, "tab_changed");
+
+	Control *tab0 = memnew(Control);
+	tab0->set_name("tab0");
+	Control *tab1 = memnew(Control);
+	tab1->set_name("tab1");
+	Control *tab2 = memnew(Control);
+	tab2->set_name("tab2");
+
+	SUBCASE("[TabContainer] add tabs by adding children") {
+		CHECK(tab_container->get_tab_count() == 0);
+		CHECK(tab_container->get_current_tab() == -1);
+		CHECK(tab_container->get_previous_tab() == -1);
+
+		// Add first tab child.
+		tab_container->add_child(tab0);
+		// MessageQueue::get_singleton()->flush();
+		CHECK(tab_container->get_tab_count() == 1);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(0)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(0)));
+
+		// Add second tab child.
+		tab_container->add_child(tab1);
+		CHECK(tab_container->get_tab_count() == 2);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Check default values, the title is the name of the child.
+		CHECK(tab_container->get_tab_control(0) == tab0);
+		CHECK(tab_container->get_tab_idx_from_control(tab0) == 0);
+		CHECK(tab_container->get_tab_title(0) == "tab0");
+		CHECK(tab_container->get_tab_tooltip(0) == "");
+		CHECK_FALSE(tab_container->is_tab_disabled(0));
+		CHECK_FALSE(tab_container->is_tab_hidden(0));
+
+		CHECK(tab_container->get_tab_control(1) == tab1);
+		CHECK(tab_container->get_tab_idx_from_control(tab1) == 1);
+		CHECK(tab_container->get_tab_title(1) == "tab1");
+		CHECK(tab_container->get_tab_tooltip(1) == "");
+		CHECK_FALSE(tab_container->is_tab_disabled(1));
+		CHECK_FALSE(tab_container->is_tab_hidden(1));
+	}
+
+	SUBCASE("[TabContainer] remove tabs by removing children") {
+		tab_container->add_child(tab0);
+		tab_container->add_child(tab1);
+		tab_container->add_child(tab2);
+		tab_container->set_current_tab(1);
+		CHECK(tab_container->get_tab_count() == 3);
+		CHECK(tab_container->get_current_tab() == 1);
+		CHECK(tab_container->get_previous_tab() == 0);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		// Remove first tab.
+		tab_container->remove_child(tab0);
+		CHECK(tab_container->get_tab_count() == 2);
+		CHECK(tab_container->get_tab_title(0) == "tab1");
+		CHECK(tab_container->get_tab_title(1) == "tab2");
+		CHECK(tab_container->get_tab_idx_from_control(tab1) == 0);
+		CHECK(tab_container->get_tab_idx_from_control(tab2) == 1);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == 0);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Remove last tab.
+		tab_container->remove_child(tab2);
+		CHECK(tab_container->get_tab_count() == 1);
+		CHECK(tab_container->get_tab_title(0) == "tab1");
+		CHECK(tab_container->get_tab_idx_from_control(tab1) == 0);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == 0);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Remove only tab.
+		tab_container->remove_child(tab1);
+		CHECK(tab_container->get_tab_count() == 0);
+		CHECK(tab_container->get_current_tab() == -1);
+		CHECK(tab_container->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK("tab_changed", build_array(build_array(-1)));
+
+		// Remove current tab when there are other tabs.
+		tab_container->add_child(tab0);
+		tab_container->add_child(tab1);
+		tab_container->add_child(tab2);
+		tab_container->set_current_tab(1);
+		tab_container->set_current_tab(2);
+		CHECK(tab_container->get_tab_count() == 3);
+		CHECK(tab_container->get_current_tab() == 2);
+		CHECK(tab_container->get_previous_tab() == 1);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		tab_container->remove_child(tab2);
+		CHECK(tab_container->get_tab_count() == 2);
+		CHECK(tab_container->get_current_tab() == 1);
+		CHECK(tab_container->get_previous_tab() == 1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK("tab_changed", build_array(build_array(1)));
+	}
+
+	SUBCASE("[TabContainer] move tabs by moving children") {
+		tab_container->add_child(tab0);
+		tab_container->add_child(tab1);
+		tab_container->add_child(tab2);
+		tab_container->set_current_tab(1);
+		CHECK(tab_container->get_current_tab() == 1);
+		CHECK(tab_container->get_previous_tab() == 0);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+
+		// Move the first tab to the end.
+		tab_container->move_child(tab0, 2);
+		CHECK(tab_container->get_tab_idx_from_control(tab0) == 2);
+		CHECK(tab_container->get_tab_idx_from_control(tab1) == 0);
+		CHECK(tab_container->get_tab_idx_from_control(tab2) == 1);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == 2);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Move the second tab to the front.
+		tab_container->move_child(tab2, 0);
+		CHECK(tab_container->get_tab_idx_from_control(tab0) == 2);
+		CHECK(tab_container->get_tab_idx_from_control(tab1) == 1);
+		CHECK(tab_container->get_tab_idx_from_control(tab2) == 0);
+		CHECK(tab_container->get_current_tab() == 1);
+		CHECK(tab_container->get_previous_tab() == 2);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+	}
+
+	SUBCASE("[TabContainer] set current tab") {
+		tab_container->add_child(tab0);
+		tab_container->add_child(tab1);
+		tab_container->add_child(tab2);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(0)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(0)));
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab0->is_visible());
+		CHECK_FALSE(tab1->is_visible());
+		CHECK_FALSE(tab2->is_visible());
+
+		// Set the current tab.
+		tab_container->set_current_tab(1);
+		CHECK(tab_container->get_current_tab() == 1);
+		CHECK(tab_container->get_previous_tab() == 0);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(1)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(1)));
+		MessageQueue::get_singleton()->flush();
+		CHECK_FALSE(tab0->is_visible());
+		CHECK(tab1->is_visible());
+		CHECK_FALSE(tab2->is_visible());
+
+		// Set to same tab.
+		tab_container->set_current_tab(1);
+		CHECK(tab_container->get_current_tab() == 1);
+		CHECK(tab_container->get_previous_tab() == 1);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(1)));
+		SIGNAL_CHECK_FALSE("tab_changed");
+		MessageQueue::get_singleton()->flush();
+		CHECK_FALSE(tab0->is_visible());
+		CHECK(tab1->is_visible());
+		CHECK_FALSE(tab2->is_visible());
+
+		// Out of bounds.
+		ERR_PRINT_OFF;
+		tab_container->set_current_tab(-5);
+		CHECK(tab_container->get_current_tab() == 1);
+		CHECK(tab_container->get_previous_tab() == 1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+		MessageQueue::get_singleton()->flush();
+		CHECK_FALSE(tab0->is_visible());
+		CHECK(tab1->is_visible());
+		CHECK_FALSE(tab2->is_visible());
+
+		tab_container->set_current_tab(5);
+		CHECK(tab_container->get_current_tab() == 1);
+		CHECK(tab_container->get_previous_tab() == 1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+		MessageQueue::get_singleton()->flush();
+		CHECK_FALSE(tab0->is_visible());
+		CHECK(tab1->is_visible());
+		CHECK_FALSE(tab2->is_visible());
+		ERR_PRINT_ON;
+	}
+
+	SUBCASE("[TabContainer] change current tab by changing visibility of children") {
+		tab_container->add_child(tab0);
+		tab_container->add_child(tab1);
+		tab_container->add_child(tab2);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab0->is_visible());
+		CHECK_FALSE(tab1->is_visible());
+		CHECK_FALSE(tab2->is_visible());
+
+		// Show a child to make it the current tab.
+		tab1->show();
+		CHECK(tab_container->get_current_tab() == 1);
+		CHECK(tab_container->get_previous_tab() == 0);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(1)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(1)));
+		MessageQueue::get_singleton()->flush();
+		CHECK_FALSE(tab0->is_visible());
+		CHECK(tab1->is_visible());
+		CHECK_FALSE(tab2->is_visible());
+
+		// Hide the visible child to select the next tab.
+		tab1->hide();
+		CHECK(tab_container->get_current_tab() == 2);
+		CHECK(tab_container->get_previous_tab() == 1);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(2)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(2)));
+		MessageQueue::get_singleton()->flush();
+		CHECK_FALSE(tab0->is_visible());
+		CHECK_FALSE(tab1->is_visible());
+		CHECK(tab2->is_visible());
+
+		// Hide the visible child to select the previous tab if there is no next.
+		tab2->hide();
+		CHECK(tab_container->get_current_tab() == 1);
+		CHECK(tab_container->get_previous_tab() == 2);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(1)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(1)));
+		MessageQueue::get_singleton()->flush();
+		CHECK_FALSE(tab0->is_visible());
+		CHECK(tab1->is_visible());
+		CHECK_FALSE(tab2->is_visible());
+
+		// Cannot hide if there is only one valid child since deselection is not enabled.
+		tab_container->remove_child(tab1);
+		tab_container->remove_child(tab2);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == 0);
+		SIGNAL_DISCARD("tab_selected");
+		SIGNAL_DISCARD("tab_changed");
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab0->is_visible());
+
+		tab0->hide();
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == 0);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab0->is_visible());
+
+		// Can hide the last tab if deselection is enabled.
+		tab_container->set_deselect_enabled(true);
+		tab0->hide();
+		CHECK(tab_container->get_current_tab() == -1);
+		CHECK(tab_container->get_previous_tab() == 0);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(-1)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(-1)));
+		MessageQueue::get_singleton()->flush();
+		CHECK_FALSE(tab0->is_visible());
+	}
+
+	SIGNAL_UNWATCH(tab_container, "tab_selected");
+	SIGNAL_UNWATCH(tab_container, "tab_changed");
+
+	memdelete(tab2);
+	memdelete(tab1);
+	memdelete(tab0);
+	memdelete(tab_container);
+}
+
+TEST_CASE("[SceneTree][TabContainer] initialization") {
+	TabContainer *tab_container = memnew(TabContainer);
+
+	Control *tab0 = memnew(Control);
+	tab0->set_name("tab0");
+	Control *tab1 = memnew(Control);
+	tab1->set_name("tab1 ");
+	Control *tab2 = memnew(Control);
+	tab2->set_name("tab2    ");
+
+	SIGNAL_WATCH(tab_container, "tab_selected");
+	SIGNAL_WATCH(tab_container, "tab_changed");
+
+	SUBCASE("[TabContainer] add children before entering tree") {
+		CHECK(tab_container->get_current_tab() == -1);
+		CHECK(tab_container->get_previous_tab() == -1);
+
+		tab_container->add_child(tab0);
+		CHECK(tab_container->get_tab_count() == 1);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+
+		tab_container->add_child(tab1);
+		CHECK(tab_container->get_tab_count() == 2);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+
+		SceneTree::get_singleton()->get_root()->add_child(tab_container);
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab_container->get_tab_count() == 2);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+		CHECK(tab0->is_visible());
+		CHECK_FALSE(tab1->is_visible());
+	}
+
+	SUBCASE("[TabContainer] current tab can be set before children are added") {
+		// Set the current tab before there are any tabs.
+		// This queues the current tab to update on entering the tree.
+		tab_container->set_current_tab(1);
+		CHECK(tab_container->get_current_tab() == -1);
+		CHECK(tab_container->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		tab_container->add_child(tab0);
+		CHECK(tab_container->get_tab_count() == 1);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+
+		tab_container->add_child(tab1);
+		CHECK(tab_container->get_tab_count() == 2);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+
+		tab_container->add_child(tab2);
+		CHECK(tab_container->get_tab_count() == 3);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// Current tab is set when entering the tree.
+		SceneTree::get_singleton()->get_root()->add_child(tab_container);
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab_container->get_tab_count() == 3);
+		CHECK(tab_container->get_current_tab() == 1);
+		CHECK(tab_container->get_previous_tab() == 0);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(1)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(1)));
+		CHECK_FALSE(tab0->is_visible());
+		CHECK(tab1->is_visible());
+		CHECK_FALSE(tab2->is_visible());
+	}
+
+	SUBCASE("[TabContainer] cannot set current tab to an invalid value before tabs are set") {
+		tab_container->set_current_tab(100);
+		CHECK(tab_container->get_current_tab() == -1);
+		CHECK(tab_container->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		tab_container->add_child(tab0);
+		CHECK(tab_container->get_tab_count() == 1);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		tab_container->add_child(tab1);
+		CHECK(tab_container->get_tab_count() == 2);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+
+		// This will print an error message as if `set_current_tab` was called after.
+		ERR_PRINT_OFF;
+		SceneTree::get_singleton()->get_root()->add_child(tab_container);
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab_container->get_tab_count() == 2);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+		ERR_PRINT_ON;
+	}
+
+	SUBCASE("[TabContainer] children visibility before entering tree") {
+		CHECK(tab_container->get_current_tab() == -1);
+		CHECK(tab_container->get_previous_tab() == -1);
+
+		// Adding a hidden child first will change visibility because it is the current tab.
+		tab0->hide();
+		tab_container->add_child(tab0);
+		CHECK(tab_container->get_tab_count() == 1);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab0->is_visible());
+
+		// Adding a visible child after will hide it because it is not the current tab.
+		tab_container->add_child(tab1);
+		CHECK(tab_container->get_tab_count() == 2);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab0->is_visible());
+		CHECK_FALSE(tab1->is_visible());
+
+		// Can change current by showing child now after children have been added.
+		// This queues the current tab to update on entering the tree.
+		tab1->show();
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab_container->get_tab_count() == 2);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+		CHECK(tab0->is_visible());
+		CHECK(tab1->is_visible());
+
+		SceneTree::get_singleton()->get_root()->add_child(tab_container);
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab_container->get_tab_count() == 2);
+		CHECK(tab_container->get_current_tab() == 1);
+		CHECK(tab_container->get_previous_tab() == 0);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(1)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(1)));
+		CHECK_FALSE(tab0->is_visible());
+		CHECK(tab1->is_visible());
+	}
+
+	SUBCASE("[TabContainer] setting current tab and changing child visibility after adding") {
+		tab_container->add_child(tab0);
+		tab_container->add_child(tab1);
+		tab_container->add_child(tab2);
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+
+		tab2->show();
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab_container->get_tab_count() == 3);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+		SIGNAL_CHECK_FALSE("tab_selected");
+		SIGNAL_CHECK_FALSE("tab_changed");
+		CHECK(tab0->is_visible());
+		CHECK_FALSE(tab1->is_visible());
+		CHECK(tab2->is_visible());
+
+		// Whichever happens last will have priority.
+		tab_container->set_current_tab(1);
+		CHECK(tab_container->get_current_tab() == 0);
+		CHECK(tab_container->get_previous_tab() == -1);
+
+		// Current tab is set when entering the tree.
+		SceneTree::get_singleton()->get_root()->add_child(tab_container);
+		MessageQueue::get_singleton()->flush();
+		CHECK(tab_container->get_tab_count() == 3);
+		CHECK(tab_container->get_current_tab() == 1);
+		CHECK(tab_container->get_previous_tab() == 0);
+		SIGNAL_CHECK("tab_selected", build_array(build_array(1)));
+		SIGNAL_CHECK("tab_changed", build_array(build_array(1)));
+		CHECK_FALSE(tab0->is_visible());
+		CHECK(tab1->is_visible());
+		CHECK_FALSE(tab2->is_visible());
+	}
+
+	SIGNAL_UNWATCH(tab_container, "tab_selected");
+	SIGNAL_UNWATCH(tab_container, "tab_changed");
+
+	memdelete(tab2);
+	memdelete(tab1);
+	memdelete(tab0);
+	memdelete(tab_container);
+}
+
+TEST_CASE("[SceneTree][TabContainer] layout and offset") {
+	TabContainer *tab_container = memnew(TabContainer);
+	SceneTree::get_singleton()->get_root()->add_child(tab_container);
+	tab_container->set_clip_tabs(false);
+
+	Control *tab0 = memnew(Control);
+	tab0->set_name("tab0");
+	Control *tab1 = memnew(Control);
+	tab1->set_name("tab1 ");
+	Control *tab2 = memnew(Control);
+	tab2->set_name("tab2    ");
+
+	tab_container->add_child(tab0);
+	tab_container->add_child(tab1);
+	tab_container->add_child(tab2);
+
+	MessageQueue::get_singleton()->flush();
+
+	Size2 all_tabs_size = tab_container->get_size();
+	const float side_margin = tab_container->get_theme_constant("side_margin");
+
+	TabBar *tab_bar = tab_container->get_tab_bar();
+
+	Vector<Rect2> tab_rects = {
+		tab_bar->get_tab_rect(0),
+		tab_bar->get_tab_rect(1),
+		tab_bar->get_tab_rect(2)
+	};
+
+	SUBCASE("[TabContainer] tabs are arranged next to each other") {
+		// Horizontal positions are next to each other.
+		CHECK(tab_rects[0].position.x == 0);
+		CHECK(tab_rects[1].position.x == tab_rects[0].size.x);
+		CHECK(tab_rects[2].position.x == tab_rects[1].position.x + tab_rects[1].size.x);
+
+		// Fills the entire width.
+		CHECK(tab_rects[2].position.x + tab_rects[2].size.x == all_tabs_size.x - side_margin);
+
+		// Horizontal sizes are positive.
+		CHECK(tab_rects[0].size.x > 0);
+		CHECK(tab_rects[1].size.x > 0);
+		CHECK(tab_rects[2].size.x > 0);
+
+		// Vertical positions are at 0.
+		CHECK(tab_rects[0].position.y == 0);
+		CHECK(tab_rects[1].position.y == 0);
+		CHECK(tab_rects[2].position.y == 0);
+
+		// Vertical sizes are the same.
+		CHECK(tab_rects[0].size.y == tab_rects[1].size.y);
+		CHECK(tab_rects[1].size.y == tab_rects[2].size.y);
+	}
+
+	SUBCASE("[TabContainer] tab position") {
+		float tab_height = tab_rects[0].size.y;
+		Ref<StyleBox> panel_style = tab_container->get_theme_stylebox("panel_style");
+
+		// Initial position, same as top position.
+		// Tab bar is at the top.
+		CHECK(tab_bar->get_anchor(SIDE_TOP) == 0);
+		CHECK(tab_bar->get_anchor(SIDE_BOTTOM) == 0);
+		CHECK(tab_bar->get_anchor(SIDE_LEFT) == 0);
+		CHECK(tab_bar->get_anchor(SIDE_RIGHT) == 1);
+		CHECK(tab_bar->get_offset(SIDE_TOP) == 0);
+		CHECK(tab_bar->get_offset(SIDE_BOTTOM) == tab_height);
+		CHECK(tab_bar->get_offset(SIDE_LEFT) == side_margin);
+		CHECK(tab_bar->get_offset(SIDE_RIGHT) == 0);
+
+		// Child is expanded and below the tab bar.
+		CHECK(tab0->get_anchor(SIDE_TOP) == 0);
+		CHECK(tab0->get_anchor(SIDE_BOTTOM) == 1);
+		CHECK(tab0->get_anchor(SIDE_LEFT) == 0);
+		CHECK(tab0->get_anchor(SIDE_RIGHT) == 1);
+		CHECK(tab0->get_offset(SIDE_TOP) == tab_height);
+		CHECK(tab0->get_offset(SIDE_BOTTOM) == 0);
+		CHECK(tab0->get_offset(SIDE_LEFT) == 0);
+		CHECK(tab0->get_offset(SIDE_RIGHT) == 0);
+
+		// Bottom position.
+		tab_container->set_tabs_position(TabContainer::POSITION_BOTTOM);
+		CHECK(tab_container->get_tabs_position() == TabContainer::POSITION_BOTTOM);
+		MessageQueue::get_singleton()->flush();
+
+		// Tab bar is at the bottom.
+		CHECK(tab_bar->get_anchor(SIDE_TOP) == 1);
+		CHECK(tab_bar->get_anchor(SIDE_BOTTOM) == 1);
+		CHECK(tab_bar->get_anchor(SIDE_LEFT) == 0);
+		CHECK(tab_bar->get_anchor(SIDE_RIGHT) == 1);
+		CHECK(tab_bar->get_offset(SIDE_TOP) == -tab_height);
+		CHECK(tab_bar->get_offset(SIDE_BOTTOM) == 0);
+		CHECK(tab_bar->get_offset(SIDE_LEFT) == side_margin);
+		CHECK(tab_bar->get_offset(SIDE_RIGHT) == 0);
+
+		// Child is expanded and above the tab bar.
+		CHECK(tab0->get_anchor(SIDE_TOP) == 0);
+		CHECK(tab0->get_anchor(SIDE_BOTTOM) == 1);
+		CHECK(tab0->get_anchor(SIDE_LEFT) == 0);
+		CHECK(tab0->get_anchor(SIDE_RIGHT) == 1);
+		CHECK(tab0->get_offset(SIDE_TOP) == 0);
+		CHECK(tab0->get_offset(SIDE_BOTTOM) == -tab_height);
+		CHECK(tab0->get_offset(SIDE_LEFT) == 0);
+		CHECK(tab0->get_offset(SIDE_RIGHT) == 0);
+
+		// Top position.
+		tab_container->set_tabs_position(TabContainer::POSITION_TOP);
+		CHECK(tab_container->get_tabs_position() == TabContainer::POSITION_TOP);
+		MessageQueue::get_singleton()->flush();
+
+		// Tab bar is at the top.
+		CHECK(tab_bar->get_anchor(SIDE_TOP) == 0);
+		CHECK(tab_bar->get_anchor(SIDE_BOTTOM) == 0);
+		CHECK(tab_bar->get_anchor(SIDE_LEFT) == 0);
+		CHECK(tab_bar->get_anchor(SIDE_RIGHT) == 1);
+		CHECK(tab_bar->get_offset(SIDE_TOP) == 0);
+		CHECK(tab_bar->get_offset(SIDE_BOTTOM) == tab_height);
+		CHECK(tab_bar->get_offset(SIDE_LEFT) == side_margin);
+		CHECK(tab_bar->get_offset(SIDE_RIGHT) == 0);
+
+		// Child is expanded and below the tab bar.
+		CHECK(tab0->get_anchor(SIDE_TOP) == 0);
+		CHECK(tab0->get_anchor(SIDE_BOTTOM) == 1);
+		CHECK(tab0->get_anchor(SIDE_LEFT) == 0);
+		CHECK(tab0->get_anchor(SIDE_RIGHT) == 1);
+		CHECK(tab0->get_offset(SIDE_TOP) == tab_height);
+		CHECK(tab0->get_offset(SIDE_BOTTOM) == 0);
+		CHECK(tab0->get_offset(SIDE_LEFT) == 0);
+		CHECK(tab0->get_offset(SIDE_RIGHT) == 0);
+	}
+
+	memdelete(tab_container);
+}
+
+// FIXME: Add tests for mouse click, keyboard navigation, and drag and drop.
+
+} // namespace TestTabContainer
+
+#endif // TEST_TAB_CONTAINER_H

tests/test_macros.h

@@ -376,6 +376,9 @@ public:
 
 	bool check_false(const String &p_name) {
 		bool has = _signals.has(p_name);
+		if (has) {
+			MESSAGE("Signal has " << _signals[p_name] << " expected none.");
+		}
 		discard_signal(p_name);
 		return !has;
 	}

tests/test_main.cpp

@@ -138,6 +138,8 @@
 #include "tests/scene/test_color_picker.h"
 #include "tests/scene/test_graph_node.h"
 #include "tests/scene/test_option_button.h"
+#include "tests/scene/test_tab_bar.h"
+#include "tests/scene/test_tab_container.h"
 #include "tests/scene/test_text_edit.h"
 #include "tests/scene/test_tree.h"
 #endif // ADVANCED_GUI_DISABLED