Decision Trees

Visual decision trees to help you choose the right testing approach for your scenario.

1. What Should I Test?

START: I need to test...
│
├─ Component rendering?
│  │
│  ├─ Static content only?
│  │  └─→ Use assertText() / assertHtml()
│  │      Example: fixture.assertText('Hello World');
│  │
│  ├─ Dynamic content with bindings?
│  │  └─→ Test initial state + binding updates
│  │      Example: component.value = 'new'; assertText('new');
│  │
│  └─ Conditional rendering (if/show)?
│     └─→ Test both shown and hidden states
│         Example: component.show = false; assertHtml('');
│
├─ User interactions?
│  │
│  ├─ Form inputs?
│  │  └─→ See Decision Tree #7
│  │
│  ├─ Button clicks?
│  │  └─→ Use trigger.click()
│  │      Example: trigger.click('button');
│  │
│  └─ Keyboard events?
│     └─→ Use trigger.keydown() / trigger.keyup()
│         Example: trigger.keydown('input', { key: 'Enter' });
│
├─ Component lifecycle?
│  │
│  └─→ Track hook calls with flags
│      Example:
│      const calls = [];
│      class { binding() { calls.push('binding'); } }
│
├─ Data fetching / async operations?
│  │
│  └─→ See Decision Tree #5
│
├─ Component with dependencies?
│  │
│  └─→ See Decision Tree #3
│
├─ Routing behavior?
│  │
│  ├─ Navigation?
│  │  └─→ Test router.load() and currentRoute
│  │
│  ├─ Route parameters?
│  │  └─→ Test params passed to component
│  │
│  └─ Route hooks (canLoad, loading)?
│     └─→ Invoke hooks manually or test via navigation
│
├─ State management?
│  │
│  ├─ Local component state?
│  │  └─→ Test property changes and rendering
│  │
│  ├─ @observable properties?
│  │  └─→ Test propertyChanged() callbacks
│  │      Example:
│  │      component.count = 5;
│  │      expect(component.onCountChanged).toHaveBeenCalled();
│  │
│  └─ Store/global state?
│     └─→ Mock store and test state updates
│
└─ Error handling?
   │
   └─→ Test error state and recovery
       Example:
       await component.load(); // Triggers error
       expect(component.error).toBeTruthy();

2. Which Fixture Creation Method?

START: I'm creating a test fixture...
│
├─ Simple inline template + class?
│  │
│  └─→ Use createFixture(template, class, deps)
│      Example:
│      createFixture(
│        '<div>${message}</div>',
│        class { message = 'Hi'; },
│        []
│      )
│
├─ Need to configure before building?
│  │
│  └─→ Use builder pattern with .build()
│      Example:
│      createFixture
│        .component(class App {})
│        .html`<div>Test</div>`
│        .deps(MyService)
│        .build()
│
├─ Testing existing component with template file?
│  │
│  └─→ Create wrapper with your component
│      Example:
│      createFixture
│        .html`<my-component value.bind="test"></my-component>`
│        .component(class { test = 'value'; })
│        .deps(MyComponent)
│        .build()
│
├─ Need to wait for initialization?
│  │
│  ├─ Manual control?
│  │  └─→ Use .build() and await fixture.startPromise
│  │      Example:
│  │      const fixture = createFixture.build();
│  │      // Do setup...
│  │      await fixture.startPromise;
│  │
│  └─ Automatic?
│     └─→ Use .build().started
│         Example:
│         const fixture = await createFixture
│           .html`...`
│           .build()
│           .started;
│
├─ Testing with custom configuration?
│  │
│  └─→ Use .config() in builder
│      Example:
│      createFixture
│        .component(class App {})
│        .config({
│          /* custom Aurelia config */
│        })
│        .build()
│
└─ Testing multiple related components?
   │
   └─→ Register all dependencies
       Example:
       createFixture
         .html`<parent><child></child></parent>`
         .deps(Parent, Child, SharedService)
         .build()

3. How Should I Mock Dependencies?

START: I need to mock a dependency...
│
├─ Simple service with few methods?
│  │
│  ├─ Just need a stub?
│  │  └─→ Create inline mock class
│  │      Example:
│  │      class MockService {
│  │        getData() { return 'mock data'; }
│  │      }
│  │      .deps(Registration.instance(IService, new MockService()))
│  │
│  └─ Need to verify calls?
│     └─→ Use createSpy() or track calls manually
│         Example:
│         const spy = createSpy();
│         class MockService {
│           getData = spy;
│         }
│
├─ Complex service with many methods?
│  │
│  ├─ Only mocking some methods?
│  │  └─→ Extend real service, override specific methods
│  │      Example:
│  │      class PartialMock extends RealService {
│  │        getData() { return 'mock'; } // Override
│  │      }
│  │
│  └─ Mocking entire service?
│     └─→ Use provided mock from @aurelia/testing
│         Example:
│         import { MockServiceLocator } from '@aurelia/testing';
│
├─ Need to change mock behavior during test?
│  │
│  └─→ Create mock with changeable state
│      Example:
│      const mockData = { value: 'initial' };
│      class MockService {
│        getData() { return mockData.value; }
│      }
│      // In test:
│      mockData.value = 'changed';
│
├─ Mocking HTTP/Fetch calls?
│  │
│  ├─ Using Aurelia Fetch Client?
│  │  └─→ Mock IHttpClient
│  │      Example:
│  │      class MockHttpClient {
│  │        fetch() { return Promise.resolve(mockResponse); }
│  │      }
│  │
│  └─ Using native fetch?
│     └─→ Mock global fetch
│         Example:
│         global.fetch = jest.fn(() =>
│           Promise.resolve({
│             json: () => Promise.resolve(mockData)
│           })
│         );
│
├─ Mocking Event Aggregator?
│  │
│  └─→ Track subscriptions and publishes
│      Example:
│      const published = [];
│      class MockEA {
│        publish(event, data) { published.push({ event, data }); }
│        subscribe() { return { dispose: () => {} }; }
│      }
│
└─ Mocking Router?
   │
   └─→ Mock IRouter with navigation tracking
       Example:
       const navigations = [];
       class MockRouter {
         load(path) {
           navigations.push(path);
           return Promise.resolve(true);
         }
       }

4. Which Assertion Method?

START: I want to assert...
│
├─ Text content?
│  │
│  ├─ Exact match of entire element?
│  │  └─→ assertText(text)
│  │      Example: assertText('Expected text');
│  │
│  ├─ Exact match of specific element?
│  │  └─→ assertText(selector, text)
│  │      Example: assertText('.title', 'Page Title');
│  │
│  ├─ Contains substring?
│  │  └─→ assertTextContain(text)
│  │      Example: assertTextContain('partial');
│  │
│  └─ Complex text verification?
│     └─→ Use getBy() + expect()
│         Example: expect(getBy('.el').textContent).toMatch(/regex/);
│
├─ HTML structure?
│  │
│  ├─ Exact innerHTML?
│  │  └─→ assertHtml(html)
│  │      Example: assertHtml('<div>Content</div>');
│  │
│  └─ Specific element's innerHTML?
│     └─→ assertHtml(selector, html)
│         Example: assertHtml('.container', '<span>Text</span>');
│
├─ CSS classes?
│  │
│  ├─ Has specific classes (can have others)?
│  │  └─→ assertClass(selector, ...classes)
│  │      Example: assertClass('.btn', 'active', 'primary');
│  │
│  └─ Has ONLY these classes?
│     └─→ assertClassStrict(selector, ...classes)
│         Example: assertClassStrict('.btn', 'active');
│
├─ Attributes?
│  │
│  ├─ Regular attribute?
│  │  └─→ assertAttr(selector, name, value)
│  │      Example: assertAttr('a', 'href', '/home');
│  │
│  └─ Namespaced attribute (SVG, XML)?
│     └─→ assertAttrNS(selector, ns, name, value)
│         Example: assertAttrNS('svg', 'http://...', 'viewBox', '0 0 100 100');
│
├─ Styles?
│  │
│  ├─ Computed styles?
│  │  └─→ assertStyles(selector, { prop: value })
│  │      Example: assertStyles('.el', { color: 'rgb(255, 0, 0)' });
│  │
│  └─ Inline styles?
│     └─→ Use getBy() + check style attribute
│         Example: expect(getBy('.el').style.color).toBe('red');
│
├─ Form values?
│  │
│  ├─ Input/textarea value?
│  │  └─→ assertValue(selector, value)
│  │      Example: assertValue('input', 'john');
│  │
│  └─ Checkbox/radio checked state?
│     └─→ assertChecked(selector, boolean)
│         Example: assertChecked('input[type=checkbox]', true);
│
├─ DOM state?
│  │
│  ├─ Element exists?
│  │  └─→ Use getBy() (throws if not found)
│  │      Example: expect(() => getBy('.el')).not.toThrow();
│  │
│  ├─ Element might not exist?
│  │  └─→ Use queryBy() (returns null)
│  │      Example: expect(queryBy('.optional')).toBeNull();
│  │
│  └─ Multiple elements?
│     └─→ Use getAllBy()
│         Example: expect(getAllBy('.item').length).toBe(3);
│
└─ Component state?
   │
   └─→ Access component directly
       Example: expect(fixture.component.value).toBe('test');

5. How to Test Async Behavior?

START: My component does async work...
│
├─ In which lifecycle hook?
│  │
│  ├─ binding() / bound()?
│  │  └─→ Await .started (hooks complete before started resolves)
│  │      Example:
│  │      const fixture = await createFixture
│  │        .component(class { async binding() { /* ... */ } })
│  │        .build()
│  │        .started;
│  │      // binding() already complete here
│  │
│  ├─ attaching() / attached()?
│  │  └─→ Await .started (attaching awaited, attached called after)
│  │      Example:
│  │      const fixture = await createFixture
│  │        .component(class { async attached() { /* ... */ } })
│  │        .build()
│  │        .started;
│  │      // attached() already complete here
│  │
│  └─ Custom method?
│     └─→ Await the method directly
│         Example:
│         await component.loadData();
│         expect(component.data).toBeTruthy();
│
├─ Using Promises?
│  │
│  ├─ Need to wait for specific promise?
│  │  └─→ Await the promise
│  │      Example:
│  │      const result = await component.fetchData();
│  │      expect(result).toBe('data');
│  │
│  └─ Testing promise rejection?
│     └─→ Use try/catch or expect().rejects
│         Example:
│         await expect(component.failingMethod()).rejects.toThrow();
│
├─ Using task queue?
│  │
│  ├─ Single task?
│  │  └─→ Await platform.taskQueue.yield()
│  │      Example:
│  │      component.queueUpdate();
│  │      await platform.taskQueue.yield();
│  │      assertText('updated');
│  │
│  └─ Multiple tasks?
│     └─→ Keep yielding until complete
│         Example:
│         while (!component.done) {
│           await platform.taskQueue.yield();
│         }
│
├─ Using setTimeout/setInterval?
│  │
│  ├─ With Jest?
│  │  └─→ Use jest.useFakeTimers()
│  │      Example:
│  │      jest.useFakeTimers();
│  │      component.startTimer();
│  │      jest.advanceTimersByTime(1000);
│  │      expect(component.ticks).toBe(1);
│  │
│  └─ With real timers?
│     └─→ Use Promise + setTimeout
│         Example:
│         await new Promise(resolve => setTimeout(resolve, 100));
│         expect(component.data).toBeTruthy();
│
├─ Waiting for DOM updates?
│  │
│  └─→ Await platform.domQueue.yield()
│      Example:
│      component.items.push('new');
│      await platform.domQueue.yield();
│      assertText('new');
│
└─ Testing loading states?
   │
   └─→ Test before and after async completion
       Example:
       const loadPromise = component.loadData();
       expect(component.loading).toBe(true); // Before
       await loadPromise;
       expect(component.loading).toBe(false); // After
       expect(component.data).toBeTruthy();

6. Which Lifecycle Hook to Test In?

START: When should I test...
│
├─ Initial component state?
│  │
│  └─→ After .started (all hooks complete)
│      Example:
│      const fixture = await createFixture.build().started;
│      expect(fixture.component.initialized).toBe(true);
│
├─ Bindable property setting?
│  │
│  └─→ In binding() or later
│      Bindables are set before binding()
│      Example:
│      class {
│        @bindable value;
│        binding() {
│          // value is available here
│        }
│      }
│
├─ DOM measurements?
│  │
│  └─→ In attached() or later
│      DOM is in document and laid out
│      Example:
│      class {
│        attached() {
│          this.width = this.element.offsetWidth; // Valid
│        }
│      }
│
├─ Event listener setup?
│  │
│  └─→ In attached()
│      Example:
│      class {
│        attached() {
│          this.element.addEventListener('click', this.handler);
│        }
│        detaching() {
│          this.element.removeEventListener('click', this.handler);
│        }
│      }
│
├─ Data fetching?
│  │
│  ├─ With router?
│  │  └─→ In loading() hook (router lifecycle)
│  │      Example:
│  │      class {
│  │        async loading(params) {
│  │          this.data = await fetch(`/api/${params.id}`);
│  │        }
│  │      }
│  │
│  └─ Without router?
│     └─→ In attached() or custom method
│         Example:
│         class {
│           async attached() {
│             await this.loadData();
│           }
│         }
│
├─ Cleanup/disposal?
│  │
│  ├─ Temporary (might reactivate)?
│  │  └─→ In detaching()
│  │      Example:
│  │      class {
│  │        detaching() {
│  │          this.stopAnimation();
│  │        }
│  │      }
│  │
│  └─ Permanent (never reactivates)?
│     └─→ In dispose()
│         Example:
│         class {
│           dispose() {
│             this.subscription.dispose();
│           }
│         }
│
└─ Observing property changes?
   │
   └─→ Use @observable with propertyChanged callback
       Example:
       class {
         @observable count = 0;
         countChanged(newValue, oldValue) {
           this.logChange(newValue, oldValue);
         }
       }

7. How to Handle User Interactions?

START: I need to simulate...
│
├─ Clicking?
│  │
│  ├─ Simple click?
│  │  └─→ trigger.click(selector)
│  │      Example:
│  │      trigger.click('button');
│  │      expect(component.clicked).toBe(true);
│  │
│  └─ Click with event options?
│     └─→ trigger.click(selector, init)
│         Example:
│         trigger.click('button', { bubbles: true });
│
├─ Typing text?
│  │
│  ├─ Single input?
│  │  └─→ type(selector, value)
│  │      Example:
│  │      type('input', 'hello');
│  │      expect(component.value).toBe('hello');
│  │
│  └─ Multiple characters with events?
│     └─→ Trigger keydown/keyup for each
│         Example:
│         for (const char of 'hello') {
│           trigger.keydown('input', { key: char });
│           trigger.keyup('input', { key: char });
│         }
│
├─ Keyboard shortcuts?
│  │
│  └─→ trigger.keydown(selector, { key, code, ... })
│      Example:
│      trigger.keydown('input', { key: 'Enter', code: 'Enter' });
│      trigger.keydown('textarea', { key: 'Escape' });
│      trigger.keydown('input', { key: 's', ctrlKey: true }); // Ctrl+S
│
├─ Form interactions?
│  │
│  ├─ Text input?
│  │  └─→ type() + verify binding
│  │      Example:
│  │      type('input[name="email"]', '[email protected]');
│  │      expect(component.email).toBe('[email protected]');
│  │
│  ├─ Checkbox?
│  │  └─→ trigger.click()
│  │      Example:
│  │      trigger.click('input[type="checkbox"]');
│  │      expect(component.agreed).toBe(true);
│  │
│  ├─ Radio button?
│  │  └─→ trigger.click()
│  │      Example:
│  │      trigger.click('input[value="option2"]');
│  │      expect(component.choice).toBe('option2');
│  │
│  ├─ Select dropdown?
│  │  └─→ Set value + trigger change
│  │      Example:
│  │      const select = getBy('select');
│  │      select.value = 'option2';
│  │      trigger('select', new Event('change'));
│  │      expect(component.selected).toBe('option2');
│  │
│  └─ Form submission?
│     └─→ trigger('form', new Event('submit'))
│         Example:
│         trigger('form', new Event('submit'));
│         expect(component.submitted).toBe(true);
│
├─ Mouse events?
│  │
│  └─→ Use trigger with MouseEvent
│      Example:
│      trigger('.draggable', new MouseEvent('mousedown', {
│        clientX: 100,
│        clientY: 100
│      }));
│
├─ Scroll events?
│  │
│  └─→ Use scrollBy helper
│      Example:
│      scrollBy('.scrollable', { top: 100 });
│      expect(component.scrolled).toBe(true);
│
├─ Custom events?
│  │
│  └─→ Use createEvent + trigger
│      Example:
│      const event = createEvent('my-event', {
│        detail: { data: 'test' }
│      });
│      trigger('.element', event);
│      expect(component.eventData).toBe('test');
│
└─ Focus/blur?
   │
   └─→ Use element.focus() / element.blur() + trigger
       Example:
       const input = getBy('input');
       input.focus();
       trigger('input', new Event('focus'));
       expect(component.focused).toBe(true);

8. Should I Write a Unit Test or Integration Test?

START: What type of test should I write?
│
├─ Testing pure logic (no DOM, no Aurelia)?
│  │
│  └─→ UNIT TEST (no fixture needed)
│      Example:
│      class Calculator {
│        add(a, b) { return a + b; }
│      }
│
│      test('adds numbers', () => {
│        const calc = new Calculator();
│        expect(calc.add(2, 3)).toBe(5);
│      });
│
├─ Testing service with no dependencies?
│  │
│  └─→ UNIT TEST (instantiate directly)
│      Example:
│      class DataService {
│        getData() { return ['a', 'b']; }
│      }
│
│      test('returns data', () => {
│        const service = new DataService();
│        expect(service.getData()).toEqual(['a', 'b']);
│      });
│
├─ Testing service with dependencies?
│  │
│  ├─ Dependencies are simple?
│  │  └─→ UNIT TEST with mocks
│  │      Example:
│  │      class UserService {
│  │        constructor(private http: HttpClient) {}
│  │        getUser(id) { return this.http.get(`/users/${id}`); }
│  │      }
│  │
│  │      test('fetches user', () => {
│  │        const mockHttp = { get: jest.fn(() => Promise.resolve({})) };
│  │        const service = new UserService(mockHttp);
│  │        service.getUser(1);
│  │        expect(mockHttp.get).toHaveBeenCalledWith('/users/1');
│  │      });
│  │
│  └─ Dependencies are complex/many?
│     └─→ INTEGRATION TEST with fixture
│         Use createFixture with DI container
│
├─ Testing component rendering?
│  │
│  └─→ INTEGRATION TEST (need template + binding)
│      Example:
│      const fixture = await createFixture
│        .html`<div>${message}</div>`
│        .component(class { message = 'Hi'; })
│        .build()
│        .started;
│      fixture.assertText('Hi');
│
├─ Testing component + child components?
│  │
│  └─→ INTEGRATION TEST (test hierarchy)
│      Example:
│      const fixture = await createFixture
│        .html`<parent><child></child></parent>`
│        .deps(Parent, Child)
│        .build()
│        .started;
│
├─ Testing custom attribute?
│  │
│  └─→ INTEGRATION TEST (need host element)
│      Example:
│      const fixture = await createFixture
│        .html`<div my-attr.bind="value"></div>`
│        .component(class { value = 'test'; })
│        .deps(MyAttr)
│        .build()
│        .started;
│
├─ Testing value converter?
│  │
│  ├─ Simple transformation (no dependencies)?
│  │  └─→ UNIT TEST (call toView/fromView directly)
│  │      Example:
│  │      class UppercaseValueConverter {
│  │        toView(value) { return value.toUpperCase(); }
│  │      }
│  │
│  │      test('uppercases', () => {
│  │        const vc = new UppercaseValueConverter();
│  │        expect(vc.toView('hello')).toBe('HELLO');
│  │      });
│  │
│  └─ Complex transformation (with dependencies)?
│     └─→ INTEGRATION TEST (test in binding)
│         Example:
│         const fixture = await createFixture
│           .html`<div>${value | myConverter}</div>`
│           .deps(MyConverter, dependencies...)
│           .build()
│           .started;
│
└─ Testing routing behavior?
   │
   └─→ INTEGRATION TEST (need router + components)
       Example:
       const fixture = await createFixture
         .component(class App {
           static routes = [{ path: 'home', component: Home }];
         })
         .html`<au-viewport></au-viewport>`
         .deps(Home)
         .build()
         .started;

Summary

These decision trees should help you:

Choose what to test based on your requirements
Select the right fixture creation method for your scenario
Mock dependencies appropriately based on complexity
Use the correct assertion method for your verification
Handle async behavior correctly
Test in the right lifecycle hook for your needs
Simulate user interactions accurately
Decide between unit and integration tests

For more detailed information, see:

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Table of Contents

1. What Should I Test?

2. Which Fixture Creation Method?

3. How Should I Mock Dependencies?

4. Which Assertion Method?

5. How to Test Async Behavior?

6. Which Lifecycle Hook to Test In?

7. How to Handle User Interactions?

8. Should I Write a Unit Test or Integration Test?

Summary