Evaluating the functionality of a pipeline that relies on various services

Question

Evaluating the functionality of a pipeline that relies on various services

There is a custom pipe in my Angular application that sanitizes HTML, defined as follows:

import { Pipe, PipeTransform } from '@angular/core';
import { DomSanitizer } from '@angular/platform-browser';

@Pipe({
    name: 'sanitiseHtml'
})

export class SanitiseHtmlPipe implements PipeTransform {

constructor(private _sanitizer: DomSanitizer) {}

    transform(value: any): any {
      return this._sanitizer.bypassSecurityTrustHtml(value);
    }

}

I am trying to write a test for this pipe like so:

describe('Pipe: Sanitizer', () => {
    let pipe: SanitiseHtmlPipe;

    beforeEach(() => {
        pipe = new SanitiseHtmlPipe(new DomSanitizer());
    });

    it('should create an instance', () => {
        expect(pipe).toBeTruthy();
    }); 
});

The issue I am facing is with the abstract class DomSanatizer which is injected into the constructor like this:

constructor(private _sanitizer: DomSanitizer) {}

Currently, I am getting a TypeScript error stating:

Cannot create an instance of the abstract class 'DomSanitizer'.

I am unsure how TypeScript handles dependency injection in Angular constructors. Does anyone have insights on how to properly test a scenario like this?

angular typescript dependency-injection angular2-testing angular-test

Answer 1

Answer №1

In order to address the DI present in your pipeline, it is essential to set up a testing environment (test bed) for resolving the dependency:

import { BrowserModule, DomSanitizer } from '@angular/platform-browser';
import { inject, TestBed } from '@angular/core/testing';

describe('SanitiseHtmlPipe', () => {
  beforeEach(() => {
    TestBed
      .configureTestingModule({
        imports: [
          BrowserModule
        ]
      });
  });

  it('create an instance', inject([DomSanitizer], (domSanitizer: DomSanitizer) => {
    let pipe = new SanitiseHtmlPipe(domSanitizer);
    expect(pipe).toBeTruthy();
  })); 
});

Answer 2

In order to address the DI present in your pipeline, it is essential to set up a testing environment (test bed) for resolving the dependency:

import { BrowserModule, DomSanitizer } from '@angular/platform-browser';
import { inject, TestBed } from '@angular/core/testing';

describe('SanitiseHtmlPipe', () => {
  beforeEach(() => {
    TestBed
      .configureTestingModule({
        imports: [
          BrowserModule
        ]
      });
  });

  it('create an instance', inject([DomSanitizer], (domSanitizer: DomSanitizer) => {
    let pipe = new SanitiseHtmlPipe(domSanitizer);
    expect(pipe).toBeTruthy();
  })); 
});

Answer 3

Answer №2

If you wish to reuse the Pipe constructor, using TestBed is a viable option:

// Reusing the Pipe constructor with TestBed
let pipe: SafeHtmlPipe;
let sanitized: DomSanitizer

beforeEach(async() => {
  TestBed.configureTestingModule({
    providers: [DomSanitizer]
  });
  sanitized = TestBed.get(DomSanitizer);
  pipe = new SafeHtmlPipe(sanitized);
});

it('should create an instance', () => {
  expect(pipe).toBeTruthy();
});

Answer 4

If you wish to reuse the Pipe constructor, using TestBed is a viable option:

// Reusing the Pipe constructor with TestBed
let pipe: SafeHtmlPipe;
let sanitized: DomSanitizer

beforeEach(async() => {
  TestBed.configureTestingModule({
    providers: [DomSanitizer]
  });
  sanitized = TestBed.get(DomSanitizer);
  pipe = new SafeHtmlPipe(sanitized);
});

it('should create an instance', () => {
  expect(pipe).toBeTruthy();
});

Answer 5

Answer №3

If you're looking to test without using the constructor, here's how I mock providers (using Jest but you can swap out with jasmine.createSpyObj):

Testing Setup

describe("MyPipe", () => {
  let pipe: MyPipe;
  const myServiceSpy = { myFunction: jest.fn() };

  beforeEach(() => {
    jest.clearAllMocks();
    TestBed.configureTestingModule({
      providers: [
        MyPipe,
        {
          provide: MyService,
          useValue: myServiceSpy
        }
      ]
    });

    pipe = TestBed.inject(myPipe);
  });

  it("should create an instance of MyPipe", () => {
    expect(pipe).toBeTruthy();
  });
});

Custom Pipe Definition

@Pipe({
  name: "myPipe"
})
export class MyPipe implements PipeTransform {
  constructor(private readonly myService: MyService) {}

  transform(value: Item): boolean {
    // perform operations with your service here
    return true;
  }
}

Answer 6

If you're looking to test without using the constructor, here's how I mock providers (using Jest but you can swap out with jasmine.createSpyObj):

Testing Setup

describe("MyPipe", () => {
  let pipe: MyPipe;
  const myServiceSpy = { myFunction: jest.fn() };

  beforeEach(() => {
    jest.clearAllMocks();
    TestBed.configureTestingModule({
      providers: [
        MyPipe,
        {
          provide: MyService,
          useValue: myServiceSpy
        }
      ]
    });

    pipe = TestBed.inject(myPipe);
  });

  it("should create an instance of MyPipe", () => {
    expect(pipe).toBeTruthy();
  });
});

Custom Pipe Definition

@Pipe({
  name: "myPipe"
})
export class MyPipe implements PipeTransform {
  constructor(private readonly myService: MyService) {}

  transform(value: Item): boolean {
    // perform operations with your service here
    return true;
  }
}

Evaluating the functionality of a pipeline that relies on various services

Answer №1

Answer №2

Answer №3

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