Add test for standard_fab_location.0.dart (flutter#149225)

Contributes to flutter#130459

It adds a test for
- `examples/api/lib/material/floating_action_button_location/standard_fab_location.0.dart`

Author: ValentinVignal

dev/bots/check_code_samples.dart

@@ -323,7 +323,6 @@ final Set<String> _knownMissingTests = <String>{
   'examples/api/test/material/menu_anchor/menu_anchor.2_test.dart',
   'examples/api/test/material/stepper/stepper.controls_builder.0_test.dart',
   'examples/api/test/material/flexible_space_bar/flexible_space_bar.0_test.dart',
-  'examples/api/test/material/floating_action_button_location/standard_fab_location.0_test.dart',
   'examples/api/test/material/chip/deletable_chip_attributes.on_deleted.0_test.dart',
   'examples/api/test/material/icon_button/icon_button.3_test.dart',
   'examples/api/test/material/expansion_panel/expansion_panel_list.expansion_panel_list_radio.0_test.dart',

examples/api/test/material/floating_action_button_location/standard_fab_location.0_test.dart

@@ -0,0 +1,20 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:flutter_api_samples/material/floating_action_button_location/standard_fab_location.0.dart'
+    as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('The FloatingActionButton should have a right padding', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.StandardFabLocationExampleApp(),
+    );
+
+    expect(find.widgetWithIcon(FloatingActionButton, Icons.add), findsOne);
+    final double right = tester.getCenter(find.byType(FloatingActionButton)).dx;
+    expect(right, closeTo(706, 1));
+  });
+}