Add tests for form_text_field.1.dart (flutter#150481)

Contributes to flutter#130459

It adds a test for
- `examples/api/lib/material/text_form_field/text_form_field.1.dart`

dev/bots/check_code_samples.dart

@@ -325,7 +325,6 @@ final Set<String> _knownMissingTests = <String>{
   'examples/api/test/material/flexible_space_bar/flexible_space_bar.0_test.dart',
   'examples/api/test/material/chip/deletable_chip_attributes.on_deleted.0_test.dart',
   'examples/api/test/material/expansion_panel/expansion_panel_list.expansion_panel_list_radio.0_test.dart',
-  'examples/api/test/material/text_form_field/text_form_field.1_test.dart',
   'examples/api/test/material/scrollbar/scrollbar.1_test.dart',
   'examples/api/test/material/search_anchor/search_anchor.0_test.dart',
   'examples/api/test/material/search_anchor/search_anchor.1_test.dart',

examples/api/test/material/text_form_field/text_form_field.1_test.dart

@@ -0,0 +1,58 @@
+// 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/services.dart';
+import 'package:flutter_api_samples/material/text_form_field/text_form_field.1.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Pressing space should focus the next field', (WidgetTester tester) async {
+    await tester.pumpWidget(const example.TextFormFieldExampleApp());
+    final Finder textFormField = find.byType(TextFormField);
+
+    expect(textFormField, findsExactly(5));
+
+    final Finder editableText = find.byType(EditableText);
+    expect(editableText, findsExactly(5));
+
+    List<bool> getFocuses() {
+      return editableText.evaluate()
+        .map((Element finderResult) => (finderResult.widget as EditableText).focusNode.hasFocus)
+        .toList();
+    }
+
+    expect(getFocuses(), const <bool>[false, false, false, false, false]);
+
+    await tester.tap(textFormField.first);
+    await tester.pump();
+
+    expect(getFocuses(), const <bool>[true, false, false, false, false]);
+
+    await tester.sendKeyEvent(LogicalKeyboardKey.space);
+    await tester.pump();
+
+    expect(getFocuses(), const <bool>[false, true, false, false, false]);
+
+    await tester.sendKeyEvent(LogicalKeyboardKey.space);
+    await tester.pump();
+
+    expect(getFocuses(), const <bool>[false, false, true, false, false]);
+
+    await tester.sendKeyEvent(LogicalKeyboardKey.space);
+    await tester.pump();
+
+    expect(getFocuses(), const <bool>[false, false, false, true, false]);
+
+    await tester.sendKeyEvent(LogicalKeyboardKey.space);
+    await tester.pump();
+
+    expect(getFocuses(), const <bool>[false, false, false, false, true]);
+
+    await tester.sendKeyEvent(LogicalKeyboardKey.space);
+    await tester.pump();
+
+    expect(getFocuses(), const <bool>[true, false, false, false, false]);
+  });
+}