astro44/test-create-fixture-flutter

test-create-fixture-flutter - Flutter Widget Test Fixture Creator

Creates Flutter widget_test fixtures for UI components. Used by dev agents during TDD to create isolated test files before implementation.

Platform: Flutter (Dart) Test Framework: flutter_test + golden_toolkit

Input Schema

{
  "project_dir": "/path/to/flutter_project",
  "ticket_id": "TICKET-XXX_A.1",
  "component_path": "lib/widgets/impact/metric_card.dart",
  "fixture_path": "test/widgets/metric_card_test.dart",
  "component_name": "MetricCard",
  "widget_class": "MetricCard",
  "acceptance_criteria": [
    {"id": "AC-001", "description": "Counter animates from 0 to target"},
    {"id": "AC-002", "description": "Displays unit label correctly"}
  ],
  "devices": ["phone", "tablet"],
  "themes": ["light", "dark"]
}

Prerequisites

Ensure pubspec.yaml includes:

dev_dependencies:
  flutter_test:
    sdk: flutter
  golden_toolkit: ^0.15.0

Instructions

1. Locate Templates

# Fixture template location (in order of priority):
# 1. Project-specific: {project_dir}/templates/tests/widget_test.template.dart
# 2. Harness: {project_dir}/harness/templates/widget_test.template.dart
# 3. Global: templates/project/tests/flutter/widget_test.template.dart

2. Process Template Variables

Replace mustache-style variables in templates:

| Variable | Source | Example | |----------|--------|---------| | {{TICKET_ID}} | input.ticket_id | TICKET-OXY-003_A.1 | | {{COMPONENT_NAME}} | input.component_name | MetricCard | | {{WIDGET_CLASS}} | input.widget_class | MetricCard | | {{COMPONENT_IMPORT}} | Derived from component_path | package:app/widgets/impact/metric_card.dart | | {{#ACCEPTANCE_CRITERIA}} | Loop over ACs | Creates test sections | | {{AC_ID}} | Each AC ID | AC-001 | | {{AC_DESCRIPTION}} | Each AC description | Counter animates... | | {{#DEVICES}} | Loop over devices | Device.phone, Device.tabletLandscape | | {{#THEMES}} | Loop over themes | ThemeData.light(), ThemeData.dark() |

3. Calculate Import Path

// Convert file path to package import
// lib/widgets/impact/metric_card.dart → package:app_name/widgets/impact/metric_card.dart

String toPackageImport(String filePath, String packageName) {
  if (filePath.startsWith('lib/')) {
    return 'package:$packageName/${filePath.substring(4)}';
  }
  return filePath;
}

4. Generate AC Test Sections

For each acceptance criterion, create a test group:

group('AC-001: Counter animates from 0 to target', () {
  testWidgets('renders correctly on phone', (tester) async {
    // Test implementation
  });

  testGoldens('visual regression', (tester) async {
    // Golden test implementation
  });
});

5. Write Fixture File

// Ensure directory exists
final fixtureDir = path.dirname(fixturePath);
await Directory(fixtureDir).create(recursive: true);

// Write processed template
await File(fixturePath).writeAsString(processedTemplate);

Null-Return Handling (CRITICAL - Prevents False Positives)

Problem: Many Flutter widgets can fail silently during build. Tests that only catch exceptions will show "success" even when the widget failed to render.

Solution: Always verify widget state after pumping:

testWidgets('widget initializes correctly', (tester) async {
  await tester.pumpWidget(
    MaterialApp(
      home: Scaffold(
        body: MetricCard(value: 42, label: 'Users'),
      ),
    ),
  );

  // CRITICAL: Verify widget actually rendered (not just that no exception thrown)
  final finder = find.byType(MetricCard);
  expect(finder, findsOneWidget, reason: 'MetricCard should render');

  // Verify internal state if widget exposes it
  final state = tester.state<MetricCardState>(finder);
  expect(state.isInitialized, isTrue, reason: 'Widget should be initialized');

  // For async initialization, pump and verify
  await tester.pumpAndSettle();
  expect(find.text('42'), findsOneWidget, reason: 'Value should display');
});

Why This Matters for Fallback Tests:

testWidgets('AC-6: Shows fallback when data loading fails', (tester) async {
  // Mock failed data source
  final mockDataSource = MockDataSource();
  when(mockDataSource.fetch()).thenThrow(Exception('Network error'));

  await tester.pumpWidget(
    MaterialApp(
      home: MetricCard(dataSource: mockDataSource),
    ),
  );
  await tester.pumpAndSettle();

  // Verify fallback UI rendered (not silent failure)
  expect(find.byType(MetricCardFallback), findsOneWidget);
  expect(find.text('Unable to load data'), findsOneWidget);
});

Output Format

{
  "skill": "test-create-fixture-flutter",
  "status": "success|failure",
  "fixture_created": "test/widgets/metric_card_test.dart",
  "template_used": "templates/project/tests/flutter/widget_test.template.dart",
  "platform": "flutter",
  "variables_replaced": {
    "TICKET_ID": "TICKET-OXY-003_A.1",
    "COMPONENT_NAME": "MetricCard",
    "COMPONENT_IMPORT": "package:oxygen_app/widgets/impact/metric_card.dart",
    "ACCEPTANCE_CRITERIA": 2,
    "DEVICES": 2,
    "THEMES": 2
  },
  "test_groups": ["AC-001", "AC-002"],
  "warnings": [],
  "next_action": "run_tests"
}

Happy Path Only (CRITICAL)

Initial fixtures focus on happy path ONLY. Edge case testing is deferred to later phases.

What to Include (Happy Path)

• Widget renders with valid props
• Standard state transitions
• Default theme rendering
• Expected device sizes

What to Defer (Edge Cases)

• Error state handling (AC descriptions mentioning "error", "failed", "missing")
• Network failure scenarios
• Null/invalid data handling
• Accessibility edge cases

Handling Edge Case ACs

When an AC describes edge case behavior, mark as deferred:

group('AC-3: Shows error state when network fails', () {
  // DEFERRED - Edge case test deferred until happy path validated
  test('deferred', () {
    // Edge case - will be implemented in augment phase
    expect(true, isTrue, reason: 'Deferred: Edge case test');
  });
});

Example Generated Fixture

// test/widgets/metric_card_test.dart
// Generated for: TICKET-OXY-003_A.1
// Component: MetricCard

import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:golden_toolkit/golden_toolkit.dart';
import 'package:oxygen_app/widgets/impact/metric_card.dart';

void main() {
  group('MetricCard - TICKET-OXY-003_A.1', () {

    // Test helpers
    Widget buildTestWidget({
      required int value,
      required String label,
      ThemeData? theme,
    }) {
      return MaterialApp(
        theme: theme ?? ThemeData.light(),
        home: Scaffold(
          body: Center(
            child: MetricCard(value: value, label: label),
          ),
        ),
      );
    }

    group('AC-001: Counter animates from 0 to target', () {
      testWidgets('renders initial state', (tester) async {
        await tester.pumpWidget(buildTestWidget(value: 100, label: 'Users'));

        // Verify widget rendered
        expect(find.byType(MetricCard), findsOneWidget);
      });

      testWidgets('animates to target value', (tester) async {
        await tester.pumpWidget(buildTestWidget(value: 100, label: 'Users'));

        // Pump through animation
        await tester.pumpAndSettle();

        // Verify final value displayed
        expect(find.text('100'), findsOneWidget);
      });

      testGoldens('visual regression - phone', (tester) async {
        await tester.pumpWidgetBuilder(
          buildTestWidget(value: 100, label: 'Users'),
          surfaceSize: Device.phone.size,
        );
        await screenMatchesGolden(tester, 'metric_card_ac001_phone');
      });
    });

    group('AC-002: Displays unit label correctly', () {
      testWidgets('shows label text', (tester) async {
        await tester.pumpWidget(buildTestWidget(value: 42, label: 'Active Users'));

        expect(find.text('Active Users'), findsOneWidget);
      });

      testGoldens('visual regression - with label', (tester) async {
        final builder = DeviceBuilder()
          ..overrideDevicesForAllScenarios(devices: [
            Device.phone,
            Device.tabletLandscape,
          ])
          ..addScenario(
            widget: buildTestWidget(value: 42, label: 'Active Users'),
            name: 'with_label',
          );

        await tester.pumpDeviceBuilder(builder);
        await screenMatchesGolden(tester, 'metric_card_ac002');
      });
    });

    // Theme testing
    group('Theme Support', () {
      testGoldens('light theme', (tester) async {
        await tester.pumpWidgetBuilder(
          buildTestWidget(value: 100, label: 'Users', theme: ThemeData.light()),
          surfaceSize: Device.phone.size,
        );
        await screenMatchesGolden(tester, 'metric_card_light');
      });

      testGoldens('dark theme', (tester) async {
        await tester.pumpWidgetBuilder(
          buildTestWidget(value: 100, label: 'Users', theme: ThemeData.dark()),
          surfaceSize: Device.phone.size,
        );
        await screenMatchesGolden(tester, 'metric_card_dark');
      });
    });
  });
}

Token Efficiency

• Template-based generation (no LLM needed for structure)
• ~2-5 second execution
• Returns ready-to-use Dart test file
• Includes golden test scaffolding for visual regression