Add unit test that proof setting TabIndex before all views are added, will have unexpected result.

UnitTests/Views/ViewTests.cs

@@ -393,6 +393,32 @@ namespace Terminal.Gui.ViewTests {
 			Assert.True (r.Subviews.IndexOf (v3) == 2);
 		}
 
+		[Fact]
+		public void TabIndex_Invert_Order_Added_One_By_One_Does_Not_Do_What_Is_Expected ()
+		{
+			var r = new View ();
+			var v1 = new View () { Id = "1", CanFocus = true };
+			r.Add (v1);
+			v1.TabIndex = 2;
+			var v2 = new View () { Id = "2", CanFocus = true };
+			r.Add (v2);
+			v2.TabIndex = 1;
+			var v3 = new View () { Id = "3", CanFocus = true };
+			r.Add (v3);
+			v3.TabIndex = 0;
+
+			Assert.False (r.TabIndexes.IndexOf (v1) == 2);
+			Assert.True (r.TabIndexes.IndexOf (v1) == 1);
+			Assert.False (r.TabIndexes.IndexOf (v2) == 1);
+			Assert.True (r.TabIndexes.IndexOf (v2) == 2);
+			// Only the last is in the expected index
+			Assert.True (r.TabIndexes.IndexOf (v3) == 0);
+
+			Assert.True (r.Subviews.IndexOf (v1) == 0);
+			Assert.True (r.Subviews.IndexOf (v2) == 1);
+			Assert.True (r.Subviews.IndexOf (v3) == 2);
+		}
+
 		[Fact]
 		public void TabIndex_Invert_Order_Mixed ()
 		{