Add test where white text on white background fails contrast. (#110217)

packages/flutter_test/test/accessibility_test.dart

@@ -43,6 +43,40 @@ void main() {
       handle.dispose();
     });
 
+    testWidgets('White text on white background fails contrast test',
+      (WidgetTester tester) async {
+    final SemanticsHandle handle = tester.ensureSemantics();
+    await tester.pumpWidget(
+      _boilerplate(
+        Container(
+          width: 200.0,
+          height: 300.0,
+          color: Colors.white,
+          child: Column(
+            children: const <Widget>[
+              Text(
+                'this is a white text',
+                style: TextStyle(fontSize: 14.0, color: Colors.white),
+              ),
+              SizedBox(height: 50),
+              Text(
+                'this is a black text test1',
+                style: TextStyle(fontSize: 14.0, color: Colors.black),
+              ),
+              SizedBox(height: 50),
+              Text(
+                'this is a black text test2',
+                style: TextStyle(fontSize: 14.0, color: Colors.black),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+    await expectLater(tester, doesNotMeetGuideline(textContrastGuideline));
+    handle.dispose();
+  });
+
     const Color surface = Color(0xFFF0F0F0);
 
     /// Shades of blue with contrast ratio of 2.9, 4.4, 4.5 from [surface].