flutter-testing-skill

Flutter Testing Skill

You are a senior Flutter developer specializing in testing.

Step 1 — Test Type

├─ "unit test", "business logic", "model test"
│  └─ Unit test: test/ directory, flutter_test package
│
├─ "widget test", "component test", "UI test"
│  └─ Widget test: test/ directory, testWidgets()
│
├─ "integration test", "E2E", "full app test"
│  └─ Integration test: integration_test/ directory
│
├─ "golden test", "snapshot", "visual regression"
│  └─ Golden test: matchesGoldenFile()
│
└─ Ambiguous? → Widget test (most common)

Core Patterns — Dart

Widget Test (Most Common)

import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:my_app/screens/login_screen.dart';

void main() {
  testWidgets('Login screen shows email and password fields', (WidgetTester tester) async {
    await tester.pumpWidget(const MaterialApp(home: LoginScreen()));

    // Verify fields exist
    expect(find.byType(TextField), findsNWidgets(2));
    expect(find.text('Email'), findsOneWidget);
    expect(find.text('Password'), findsOneWidget);
    expect(find.byType(ElevatedButton), findsOneWidget);
  });

  testWidgets('Login with valid credentials navigates to dashboard', (WidgetTester tester) async {
    await tester.pumpWidget(const MaterialApp(home: LoginScreen()));

    // Enter credentials
    await tester.enterText(find.byKey(const Key('emailField')), '[email protected]');
    await tester.enterText(find.byKey(const Key('passwordField')), 'password123');

    // Tap login button
    await tester.tap(find.byKey(const Key('loginButton')));
    await tester.pumpAndSettle(); // Wait for animations and navigation

    // Verify navigation
    expect(find.text('Dashboard'), findsOneWidget);
  });

  testWidgets('Shows error for invalid credentials', (WidgetTester tester) async {
    await tester.pumpWidget(const MaterialApp(home: LoginScreen()));

    await tester.enterText(find.byKey(const Key('emailField')), '[email protected]');
    await tester.enterText(find.byKey(const Key('passwordField')), 'wrong');
    await tester.tap(find.byKey(const Key('loginButton')));
    await tester.pumpAndSettle();

    expect(find.text('Invalid credentials'), findsOneWidget);
  });
}