ngx-page-object-model


ngx-page-object-model is a lightweight library designed to simplify writing unit tests for Angular UI Components by leveraging the Page Object Model (POM) design pattern.

By using the Page Object Model design pattern, you can create a new abstraction level and keep your test logic separated from the logic to read and manipulate the DOM.

This library is fully Angular-based and completely testing-framework-agnostic, making it compatible with Jasmine, Jest, Vitest, or any other unit testing framework.
It can be used alongside tools like Spectator or as a standalone solution.

Setup

``
npm install -D ngx-page-object-model
`

- Check the Documentation for more details

Basic examples

$3

In this minimalistic example, direct interaction with the DOM happens within the test itself, leading to repetition and more complex code:

`typescript
beforeEach(async () => {
// ...
fixture = TestBed.createComponent(CounterComponent);
});

it('should increase the counter when clicking on the increase button', () => {
fixture.debugElement.query(By.css(#increase-btn)).nativeElement.click();

expect(fixture.debugElement.query(By.css([data-testid="count"])).nativeElement.innerHTML).toEqual('1');
});

it('should decrease the counter if the current value is greater than 0 when clicking on the decrease button', () => {
fixture.debugElement.query(By.css(#increase-btn)).nativeElement.click();
fixture.debugElement.query(By.css(#increase-btn)).nativeElement.click();

fixture.debugElement.query(By.css(#decrease-btn)).nativeElement.click();

expect(fixture.debugElement.query(By.css([data-testid="count"])).nativeElement.innerHTML).toEqual('1');
});
`

$3

With the Page Object Model pattern, the logic to interact with the DOM is encapsulated within a dedicated page object.
This approach makes tests more readable, ensures accurate typing for HTML elements, and reduces code duplication. The page object is simply a class extending PageObjectModel:

`typescript
import { DebugHtmlElement, PageObjectModel } from 'ngx-page-object-model';

class CounterPage extends PageObjectModel {
getIncreaseButton(): DebugHtmlElement {
return this.getDebugElementByCss('#increase-btn');
}
getDecreaseButton(): DebugHtmlElement {
return this.getDebugElementByCss('#decrease-btn');
}
getCount(): DebugHtmlElement {
return this.getDebugElementByTestId('count');
}

clickIncreaseButton(): void {
this.getIncreaseButton().nativeElement.click();
}
clickDecreaseButton(): void {
this.getDecreaseButton().nativeElement.click();
}
}
`

The test code is now cleaner, more focused, and avoids repetitive DOM manipulation:

`typescript
beforeEach(async () => {
// ...
fixture = TestBed.createComponent(CounterComponent);
page = new CounterPage(fixture);
});

it('should increase the counter when clicking on the increase button', () => {
page.clickIncreaseButton();

expect(page.getCount().nativeElement.innerHTML).toEqual('1');
});

it('should decrease the counter if the current value is greater than 0 when clicking on the decrease button', () => {
page.clickIncreaseButton();
page.clickIncreaseButton();

page.clickDecreaseButton();

expect(page.getCount().nativeElement.innerHTML).toEqual('0');
});
`

More developer-friendly errors

When using Angular default methods, running into a typo in a selector usually gives you an error like this:

> TypeError: Cannot read properties of null (reading 'nativeElement')

The methods provided by ngx-page-object-model, such as getDebugElementByCss() and getDebugElementByTestId(), are instead designed to produce clearer and more descriptive error messages:

> Element with selector "#some-selector" was not found.

This makes debugging a lot smoother, helping you quickly spot and fix broken CSS selectors or incorrect data-testid values.

$3

If you want to explicitly check that an element is not present in the DOM, you can pass false to disable the default assertion error:

`typescript
// Assert that the count element is not present in the DOM
expect(page.getCount(false)).not.toBeDefined();
``

Documentation

- Check the Documentation for more code examples, features and techniques.