Update & improve `TabBar.labelColor` tests (#133668)

fixes [Improve `TabBar.labelColor` tests](https://github.com/flutter/flutter/issues/133665)

While working on a fix for https://github.com/flutter/flutter/issues/109484, I found the existing test could use some improvement first.

packages/flutter/test/material/tab_bar_theme_test.dart

@@ -1216,4 +1216,77 @@ void main() {
     tabBarBox = tester.firstRenderObject<RenderBox>(find.byType(TabBar));
     expect(tabBarBox,paints..line(color: tabBarThemeIndicatorColor));
   });
+
+   testWidgets('TabBarTheme.labelColor resolves material states', (WidgetTester tester) async {
+    const Color selectedColor = Color(0xff00ff00);
+    const Color unselectedColor = Color(0xffff0000);
+    final MaterialStateColor labelColor = MaterialStateColor.resolveWith((Set<MaterialState> states) {
+      if (states.contains(MaterialState.selected)) {
+        return selectedColor;
+      }
+      return unselectedColor;
+    });
+
+    final TabBarTheme tabBarTheme = TabBarTheme(labelColor: labelColor);
+
+    // Test labelColor correctly resolves material states.
+    await tester.pumpWidget(buildTabBar(tabBarTheme: tabBarTheme));
+
+    final IconThemeData selectedTabIcon = IconTheme.of(tester.element(find.text(_tab1Text)));
+    final IconThemeData uselectedTabIcon = IconTheme.of(tester.element(find.text(_tab2Text)));
+    final TextStyle selectedTextStyle = tester.renderObject<RenderParagraph>(find.text(_tab1Text)).text.style!;
+    final TextStyle unselectedTextStyle = tester.renderObject<RenderParagraph>(find.text(_tab2Text)).text.style!;
+
+    expect(selectedTabIcon.color, selectedColor);
+    expect(uselectedTabIcon.color, unselectedColor);
+    expect(selectedTextStyle.color, selectedColor);
+    expect(unselectedTextStyle.color, unselectedColor);
+  });
+
+  testWidgets('TabBarTheme.labelColor & TabBarTheme.unselectedLabelColor override material state TabBarTheme.labelColor',
+    (WidgetTester tester) async {
+      const Color selectedStateColor = Color(0xff00ff00);
+      const Color unselectedStateColor = Color(0xffff0000);
+      final MaterialStateColor labelColor = MaterialStateColor.resolveWith((Set<MaterialState> states) {
+        if (states.contains(MaterialState.selected)) {
+          return selectedStateColor;
+        }
+        return unselectedStateColor;
+      });
+      const Color selectedColor = Color(0xff00ffff);
+      const Color unselectedColor = Color(0xffff12ff);
+
+      TabBarTheme tabBarTheme = TabBarTheme(labelColor: labelColor);
+
+      // Test material state label color.
+      await tester.pumpWidget(buildTabBar(tabBarTheme: tabBarTheme));
+
+      IconThemeData selectedTabIcon = IconTheme.of(tester.element(find.text(_tab1Text)));
+      IconThemeData uselectedTabIcon = IconTheme.of(tester.element(find.text(_tab2Text)));
+      TextStyle selectedTextStyle = tester.renderObject<RenderParagraph>(find.text(_tab1Text)).text.style!;
+      TextStyle unselectedTextStyle = tester.renderObject<RenderParagraph>(find.text(_tab2Text)).text.style!;
+
+      expect(selectedTabIcon.color, selectedStateColor);
+      expect(uselectedTabIcon.color, unselectedStateColor);
+      expect(selectedTextStyle.color, selectedStateColor);
+      expect(unselectedTextStyle.color, unselectedStateColor);
+
+      // Test labelColor & unselectedLabelColor override material state labelColor.
+      tabBarTheme = const TabBarTheme(
+        labelColor: selectedColor,
+        unselectedLabelColor: unselectedColor,
+      );
+      await tester.pumpWidget(buildTabBar(tabBarTheme: tabBarTheme));
+      await tester.pumpAndSettle();
+
+      selectedTabIcon = IconTheme.of(tester.element(find.text(_tab1Text)));
+      uselectedTabIcon = IconTheme.of(tester.element(find.text(_tab2Text)));
+      selectedTextStyle = tester.renderObject<RenderParagraph>(find.text(_tab1Text)).text.style!;
+      unselectedTextStyle = tester.renderObject<RenderParagraph>(find.text(_tab2Text)).text.style!;
+
+      expect(selectedTabIcon.color, selectedColor);
+      expect(uselectedTabIcon.color, unselectedColor);
+      expect(selectedTextStyle.color, selectedColor);
+      expect(unselectedTextStyle.color, unselectedColor);
+  });
 }