The Problem
Imagine you're building an Angular application and need to redirect the user to an external site, like the website of the American grunge band Pearl Jam. A common way to do this is by manipulating the window object. For example, you might have a function that changes the window.location.href to redirect the user:
redirectToPearlJam() {
window.location.href = 'https://pearljam.com';
}
Now, how do we test this?
Testing the Redirect Function
Testing code that manipulates the window object can be tricky since window is a global browser API. But don't worry, there are solutions! Here are some tips to do this in a straightforward way.
1. Using Jasmine Spy
The first solution is to use Jasmine spies to monitor and intercept calls to window.location.href. Here’s how to do it:
import { ComponentFixture, TestBed } from '@angular/core/testing';
import { YourComponent } from './your-component';
describe('YourComponent', () => {
let component: YourComponent;
let fixture: ComponentFixture<YourComponent>;
beforeEach(() => {
TestBed.configureTestingModule({
declarations: [YourComponent]
}).compileComponents();
fixture = TestBed.createComponent(YourComponent);
component = fixture.componentInstance;
fixture.detectChanges();
});
it('should redirect to Pearl Jam website', () => {
spyOn(window, 'open');
component.redirectToPearlJam();
expect(window.open).toHaveBeenCalledWith('https://pearljam.com');
});
});
2. Mocking Window Object
Another way is to create a mock of the window object to use in tests. We can do this by injecting window into the component:
export function windowFactory() {
return window;
}
@NgModule({
providers: [
{ provide: 'Window', useFactory: windowFactory }
]
})
export class AppModule { }
And in the component, we use the injected object:
import { Inject, Injectable } from '@angular/core';
@Injectable({
providedIn: 'root',
})
export class YourService {
constructor(@Inject('Window') private window: Window) {}
redirectToPearlJam() {
this.window.location.href = 'https://pearljam.com';
}
}
In the test, we can create a mock of window:
import { TestBed } from '@angular/core/testing';
import { YourService } from './your-service';
describe('YourService', () => {
let service: YourService;
let mockWindow: { location: { href: string } };
beforeEach(() => {
mockWindow = { location: { href: '' } };
TestBed.configureTestingModule({
providers: [
YourService,
{ provide: 'Window', useValue: mockWindow }
]
});
service = TestBed.inject(YourService);
});
it('should redirect to Pearl Jam website', () => {
service.redirectToPearlJam();
expect(mockWindow.location.href).toEqual('https://pearljam.com');
});
});
3. Assigning Mock to Component Variable
Another approach is to create a variable inside the component that holds the window object. In the tests, we can assign a mock to this variable. Here's how to do it:
In the component, add a variable for window:
export class YourComponent {
private window: Window;
constructor() {
this.window = window;
}
redirectToPearlJam() {
this.window.location.href = 'https://pearljam.com';
}
}
In the test, we replace the component’s window variable with a mock:
import { ComponentFixture, TestBed } from '@angular/core/testing';
import { YourComponent } from './your-component';
describe('YourComponent', () => {
let component: YourComponent;
let fixture: ComponentFixture<YourComponent>;
let mockWindow: { location: { href: string } };
beforeEach(() => {
TestBed.configureTestingModule({
declarations: [YourComponent]
}).compileComponents();
fixture = TestBed.createComponent(YourComponent);
component = fixture.componentInstance;
mockWindow = { location: { href: '' } };
component['window'] = mockWindow; // Assign the mock here
fixture.detectChanges();
});
it('should redirect to Pearl Jam website', () => {
component.redirectToPearlJam();
expect(mockWindow.location.href).toEqual('https://pearljam.com');
});
});
Conclusion
Testing code that interacts with the window object in Angular might seem complicated, but with these strategies, it becomes much easier. Using Jasmine spies, creating a mock of window, or using a component variable for the window object are effective approaches that will help you keep your tests clean and functional.
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