Hide implementation details of doctest macros

`test_macros.h` is created to provide various macros acting as aliases for
doctest macros to work better with Godot internals and conventions. This also
makes it accessible for those who'd like to start writing tests in Godot, as
most vital information can be put together and documented directly in
`test_macros.h` header.

Developers are encouraged to include the new `tests/test_macros.h` for writing
new tests over `thirdparty/doctest/doctest.h`.

Added `TEST_CASE_PENDING("name")` as an alias for
`TEST_CASE("name", doctest::skip())` which could be used to mark failing tests
for issues yet to be fixed, so as to not affect CI testing results.

Added `ERR_PRINT_OFF` and `ERR_PRINT_ON` to control error printing for testing
various **expected** failure paths within Godot without polluting the test
summary with error messages.

tests/test_macros.h

@@ -0,0 +1,50 @@
+/*************************************************************************/
+/*  test_macros.h                                                        */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2020 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2020 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* 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_MACROS_H
+#define TEST_MACROS_H
+
+// See documentation for doctest at:
+// https://github.com/onqtam/doctest/blob/master/doc/markdown/readme.md#reference
+#include "thirdparty/doctest/doctest.h"
+
+// The test is skipped with this, run pending tests with `--test --no-skip`.
+#define TEST_CASE_PENDING(name) TEST_CASE(name *doctest::skip())
+
+// Temporarily disable error prints to test failure paths.
+// This allows to avoid polluting the test summary with error messages.
+// The `_print_error_enabled` boolean is defined in `core/print_string.cpp` and
+// works at global scope. It's used by various loggers in `should_log()` method,
+// which are used by error macros which call into `OS::print_error`, effectively
+// disabling any error messages to be printed from the engine side (not tests).
+#define ERR_PRINT_OFF _print_error_enabled = false;
+#define ERR_PRINT_ON _print_error_enabled = true;
+
+#endif // TEST_MACROS_H

tests/test_main.cpp

@@ -50,7 +50,7 @@
 
 #include "modules/modules_tests.gen.h"
 
-#include "thirdparty/doctest/doctest.h"
+#include "tests/test_macros.h"
 
 int test_main(int argc, char *argv[]) {
 	// Doctest runner.

tests/test_string.h

@@ -44,7 +44,7 @@
 #include "modules/regex/regex.h"
 #endif
 
-#include "thirdparty/doctest/doctest.h"
+#include "tests/test_macros.h"
 
 namespace TestString {
 

tests/test_validate_testing.h

@@ -33,10 +33,26 @@
 
 #include "core/os/os.h"
 
-#include "thirdparty/doctest/doctest.h"
+#include "tests/test_macros.h"
 
-TEST_CASE("Validate Test will always pass") {
-	CHECK(true);
+TEST_SUITE("Validate tests") {
+	TEST_CASE("Always pass") {
+		CHECK(true);
+	}
+	TEST_CASE_PENDING("Pending tests are skipped") {
+		if (!doctest::getContextOptions()->no_skip) { // Normal run.
+			FAIL("This should be skipped if `--no-skip` is NOT set (missing `doctest::skip()` decorator?)");
+		} else {
+			CHECK_MESSAGE(true, "Pending test is run with `--no-skip`");
+		}
+	}
+	TEST_CASE("Muting Godot error messages") {
+		ERR_PRINT_OFF;
+		CHECK_MESSAGE(!_print_error_enabled, "Error printing should be disabled.");
+		ERR_PRINT("Still waiting for Godot!"); // This should never get printed!
+		ERR_PRINT_ON;
+		CHECK_MESSAGE(_print_error_enabled, "Error printing should be re-enabled.");
+	}
 }
 
 #endif // TEST_VALIDATE_TESTING_H

tests/test_variant.h

@@ -34,7 +34,7 @@
 #include "core/variant.h"
 #include "core/variant_parser.h"
 
-#include "thirdparty/doctest/doctest.h"
+#include "tests/test_macros.h"
 
 namespace TestVariant {