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Structure of Component for Unit Testing in Angular

Structure of Component for Unit Testing in Angular

Owned by Aman Singh
Dec 13, 2024
2 min read

Purpose

This document provides a standardized structure for writing unit tests for Angular components. Following this structure ensures that all dependencies and data models are correctly set up, reducing the likelihood of test failures due to unconfigured services, missing providers, or improperly mocked data.

Guidelines for Component Structure

1. Data Models

  • Create or import data models required by the component. Use interfaces or classes to define the data structure.

  • Mock necessary data objects for use in unit tests.

Example:

export interface User { id: number; name: string; email: string; } const mockUser: User = { id: 1, name: 'John Doe', email: 'john.doe@example.com', };

2. Module and Component Imports

  • Ensure all necessary Angular modules, custom components, and directives are imported.

  • Use RouterTestingModule and HttpClientTestingModule where applicable.

Example:

import { ComponentFixture, TestBed } from '@angular/core/testing'; import { ReactiveFormsModule } from '@angular/forms'; import { RouterTestingModule } from '@angular/router/testing'; import { HttpClientTestingModule } from '@angular/common/http/testing'; import { MyComponent } from './my-component.component';

3. Dependencies and Providers

  • Mock all services, directives, or external dependencies used by the component.

  • Use the providers array in TestBed.configureTestingModule to add mocks.

Example:

import { MyService } from './my-service.service'; import { of } from 'rxjs'; const mockMyService = { fetchData: jasmine.createSpy('fetchData').and.returnValue(of([])), }; beforeEach(async () => { await TestBed.configureTestingModule({ declarations: [MyComponent], imports: [ReactiveFormsModule, RouterTestingModule, HttpClientTestingModule], providers: [ { provide: MyService, useValue: mockMyService }, ], }).compileComponents(); });

4. Component Initialization

  • Ensure proper initialization of the component and its inputs.

  • Use beforeEach for setting up component-specific mocks or configurations.

Example:

let component: MyComponent; let fixture: ComponentFixture<MyComponent>; beforeEach(() => { fixture = TestBed.createComponent(MyComponent); component = fixture.componentInstance; // Mock input component.inputData = mockUser; fixture.detectChanges(); });

5. Common Mock Modules

  • RouterTestingModule: For routing dependencies.

  • HttpClientTestingModule: For HTTP requests.

  • MatDialogTestingModule (or mock MatDialogRef): For Angular Material dialogs.

  • StoreModule (or mock Store): For NgRx state management.

6. Testing Utility Functions

  • Create utility functions to reduce redundant code for repetitive tasks like mocking services, handling inputs, or emitting events.

Example:

function setupMockService<T>(mockService: T): T { return mockService; } const mockServiceInstance = setupMockService(mockMyService);

7. Writing Tests

  • Test each functionality independently using it blocks.

  • Cover:

    • Component creation

    • Input and Output bindings

    • Service calls

    • UI interactions

    • Error scenarios

Example:

describe('MyComponent', () => { it('should create the component', () => { expect(component).toBeTruthy(); }); it('should fetch data on init', () => { component.ngOnInit(); expect(mockMyService.fetchData).toHaveBeenCalled(); }); it('should display user name', () => { component.user = mockUser; fixture.detectChanges(); const compiled = fixture.nativeElement; expect(compiled.querySelector('.user-name').textContent).toContain('John Doe'); }); });

Conclusion

Adhering to this structure ensures well-organized and effective unit tests, minimizing runtime errors and improving test coverage.

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