Unit Testing: Everything You Need To Know

Example of an Android unit test:

public class ExampleUnitTest {

    @Test

    public void testAddition() {

        Calculator calculator = new Calculator();

        int result = calculator.add(2, 3);

        assertEquals(5, result);

    }

    @Test

    public void testSubtraction() {

        Calculator calculator = new Calculator();

        int result = calculator.subtract(5, 2);

        assertEquals(3, result);

    }

}

In this example, we’re testing a simple Calculator class that has two methods: ‘add’ and ‘subtract’. The ‘testAddition’ method creates a new instance of the ‘Calculator’ class, calls the ‘add’ method with two parameters (2 and 3), and then checks that the result is equal to 5 using the ‘assertEquals’ method. Similarly, the ‘testSubtraction’ method tests the ‘subtract’ method with two parameters (5 and 2) and checks that the result is equal to 3.

These tests are written using the JUnit testing framework, which is commonly used for unit testing in Android development. They demonstrate the basic structure of a unit test, which involves creating an instance of the class being tested, calling its methods with various inputs, and verifying that the outputs are correct using assertion statements like ‘assertEquals’

Angular Unit Testing:

import { ComponentFixture, TestBed } from ‘@angular/core/testing’;

import { MyComponent } from ‘./my.component’;

describe(‘MyComponent’, () => {

  let component: MyComponent;

  let fixture: ComponentFixture<MyComponent>;

  beforeEach(async () => {

    await TestBed.configureTestingModule({

      declarations: [ MyComponent ]

    })

    .compileComponents();

  });

  beforeEach(() => {

    fixture = TestBed.createComponent(MyComponent);

    component = fixture.componentInstance;

    fixture.detectChanges();

  });

  it(‘should create the component’, () => {

    expect(component).toBeTruthy();

  });

  it(‘should display the correct title’, () => {

    component.title = ‘Test Title’;

    fixture.detectChanges();

    const titleElement = fixture.nativeElement.querySelector(‘h1’);

    expect(titleElement.textContent).toContain(‘Test Title’);

  });

});

In this example, we’re testing a simple Angular component called ‘MyComponent’. The ‘beforeEach’ block sets up the test environment by configuring a ‘TestBed’ instance with the ‘MyComponent’ declaration, and then compiling the component’s template. The ‘beforeEach’ block also creates a fixture object and assigns it to ‘fixture’, which we can use to access the component’s properties and methods during the tests.

The first test, ‘should create the component’, simply checks that the MyComponent instance is truthy, indicating that it has been successfully created.

The second test, ‘should display the correct title’, sets the component’s ‘title’ property to ‘Test Title’, updates the view using ‘fixture.detectChanges()’, and then uses the ‘fixture.nativeElement’ object to query the DOM for the ‘h1’ element that displays the title. The test then checks that the element’s ‘textContent’ property contains the expected value (‘Test Title’).

These tests demonstrate the basic structure of an Angular unit test, which involves creating a fixture object for the component, manipulating the component’s properties and methods, and verifying the state of the component and its view using assertions like ‘expect’.