How to test a service
The service we want to test against:
import {Injectable} from '@angular/core';
import {LoggerService} from './logger.service';
@Injectable({
providedIn: 'root'
})
export class CalculatorService {
constructor(private logger: LoggerService) {
}
add(n1: number, n2:number) {
this.logger.log("Addition operation called");
return n1 + n2;
}
subtract(n1: number, n2:number) {
this.logger.log("Subtraction operation called");
return n1 - n2;
}
}
For this service, we want to test two things:
1. add / subtract functions should return the correct values.
2. The logger service should be called only once for each method.
Using Spy to mock a service
For logger service, we don't want to call the real service, it might trigger side effects, for example, send analytics request. We want to mock a logger service:
beforeEach(()=> { loggerSpy = jasmine.createSpyObj('LoggerService', ['log']) TestBed.configureTestingModule({ providers: [ CalculatorService, // If you want to use spy, you have to use provide + useValue syntax, otherwise, Angular will init an actual // implementation of LoggerService. {provide: LoggerService, useValue: loggerSpy} ] }) calculator = TestBed.get(CalculatorService) });
Full test code:
import {CalculatorService} from './calculator.service';
import {LoggerService} from './logger.service';
import {TestBed} from '@angular/core/testing';
// fdescribe
describe('CalculatorService', () => {
let calculator: CalculatorService,
loggerSpy: any;
beforeEach(()=> {
loggerSpy = jasmine.createSpyObj('LoggerService', ['log'])
TestBed.configureTestingModule({
providers: [
CalculatorService,
// If you want to use spy, you have to use provide + useValue syntax, otherwise, Angular will init an actual
// implementation of LoggerService.
{provide: LoggerService, useValue: loggerSpy}
]
})
calculator = TestBed.get(CalculatorService)
});
// fit
it('should add two numbers', () => {
const result = calculator.add(2, 2);
expect(result).toBe(4);
expect(loggerSpy.log).toHaveBeenCalledTimes(1);
});
it('should subtract two numbers', () => {
const result = calculator.subtract(2, 2);
expect(result).toBe(0, "unexpected subtraction result");
expect(loggerSpy.log).toHaveBeenCalledTimes(1);
});
});
Testing a service with HTTP request
The service we want to test against:
import { Injectable } from "@angular/core";
import { HttpClient, HttpParams } from "@angular/common/http";
import { Observable } from "rxjs";
import { map } from "rxjs/operators";
import { Lesson } from "../model/lesson";
import { Course } from "../model/course";
@Injectable()
export class CoursesService {
constructor(private http: HttpClient) {}
findCourseById(courseId: number): Observable<Course> {
return this.http.get<Course>(`/api/courses/${courseId}`);
}
findAllCourses(): Observable<Course[]> {
return this.http.get("/api/courses").pipe(map(res => res["payload"]));
}
saveCourse(courseId: number, changes: Partial<Course>): Observable<Course> {
return this.http.put<Course>(`/api/courses/${courseId}`, changes);
}
findLessons(
courseId: number,
filter = "",
sortOrder = "asc",
pageNumber = 0,
pageSize = 3
): Observable<Lesson[]> {
return this.http
.get("/api/lessons", {
params: new HttpParams()
.set("courseId", courseId.toString())
.set("filter", filter)
.set("sortOrder", sortOrder)
.set("pageNumber", pageNumber.toString())
.set("pageSize", pageSize.toString())
})
.pipe(map(res => res["payload"]));
}
}
For this service, we also don't want to issue a real http request, therefore we also need to mock a HTTP service, Angular provides HttpClientTestingModule for us. We can use the HttpTestingController.
let coursesService: CoursesService, httpTestingController: HttpTestingController; beforeEach(() => { TestBed.configureTestingModule({ imports: [HttpClientTestingModule], providers: [CoursesService] }); (coursesService = TestBed.get(CoursesService)), (httpTestingController = TestBed.get(HttpTestingController)); });
Example code:
it("should retrieve all courses", () => { coursesService.findAllCourses().subscribe(courses => { expect(courses).toBeTruthy("No courses returned"); expect(courses.length).toBe(12, "incorrect number of courses"); const course = courses.find(course => course.id == 12); expect(course.titles.description).toBe("Angular Testing Course"); }); // expect only one request const req = httpTestingController.expectOne("/api/courses"); // check the request should be the GET request expect(req.request.method).toEqual("GET"); // issue the mock http request and return the response req.flush({ payload: Object.values(COURSES) }); });
Testing a error HTTP request
Calling 'fail' method from Jasmine in the success block, which means "This test should in Error block, but landed on Success block, so we consider the test is failed."
it("should give an error if save course fails", () => { const changes: Partial<Course> = { titles: { description: "Testing Course" } }; coursesService.saveCourse(12, changes).subscribe( () => fail("save course operation should have failed"), (error: HttpErrorResponse) => { expect(error.status).toBe(500); } ); const req = httpTestingController.expectOne("/api/courses/12"); expect(req.request.body.titles.description).toEqual("Testing Course"); expect(req.request.method).toBe("PUT"); req.flush("save course fail", { status: 500, statusText: "Internal server error" }); });
Testing HTTP params
Example Code:
it("should find a list of lessons", () => { coursesService.findLessons(12).subscribe(lessons => { expect(lessons).toBeTruthy(); expect(lessons.length).toBe(3); }); // expectOne can also take function const req = httpTestingController.expectOne( req => req.url == "/api/lessons" ); expect(req.request.method).toEqual("GET"); expect(req.request.params.get("courseId")).toEqual("12"); expect(req.request.params.get("filter")).toEqual(""); expect(req.request.params.get("sortOrder")).toEqual("asc"); expect(req.request.params.get("pageNumber")).toEqual("0"); expect(req.request.params.get("pageSize")).toEqual("3"); req.flush({ payload: findLessonsForCourse(12).slice(0, 3) }); });
--
Full testing code:
import { CoursesService } from "./courses.service";
import { TestBed } from "@angular/core/testing";
import {
HttpClientTestingModule,
HttpTestingController
} from "@angular/common/http/testing";
import { COURSES, findLessonsForCourse } from "../../../../server/db-data";
import { Course } from "../model/course";
import { HttpErrorResponse } from "@angular/common/http";
fdescribe("CoursesService", () => {
let coursesService: CoursesService,
httpTestingController: HttpTestingController;
beforeEach(() => {
TestBed.configureTestingModule({
imports: [HttpClientTestingModule],
providers: [CoursesService]
});
(coursesService = TestBed.get(CoursesService)),
(httpTestingController = TestBed.get(HttpTestingController));
});
it("should retrieve all courses", () => {
coursesService.findAllCourses().subscribe(courses => {
expect(courses).toBeTruthy("No courses returned");
expect(courses.length).toBe(12, "incorrect number of courses");
const course = courses.find(course => course.id == 12);
expect(course.titles.description).toBe("Angular Testing Course");
});
const req = httpTestingController.expectOne("/api/courses");
expect(req.request.method).toEqual("GET");
req.flush({ payload: Object.values(COURSES) });
});
it("should save the course data", () => {
const changes: Partial<Course> = {
titles: { description: "Testing Course" }
};
coursesService.saveCourse(12, changes).subscribe(course => {
expect(course.id).toEqual(12);
});
const req = httpTestingController.expectOne("/api/courses/12");
expect(req.request.body.titles.description).toEqual("Testing Course");
expect(req.request.method).toBe("PUT");
req.flush({
...COURSES[12],
...changes
});
});
it("should give an error if save course fails", () => {
const changes: Partial<Course> = {
titles: { description: "Testing Course" }
};
coursesService.saveCourse(12, changes).subscribe(
() => fail("save course operation should have failed"),
(error: HttpErrorResponse) => {
expect(error.status).toBe(500);
}
);
const req = httpTestingController.expectOne("/api/courses/12");
expect(req.request.body.titles.description).toEqual("Testing Course");
expect(req.request.method).toBe("PUT");
req.flush("save course fail", {
status: 500,
statusText: "Internal server error"
});
});
it("should find a list of lessons", () => {
coursesService.findLessons(12).subscribe(lessons => {
expect(lessons).toBeTruthy();
expect(lessons.length).toBe(3);
});
const req = httpTestingController.expectOne(
req => req.url == "/api/lessons"
);
expect(req.request.method).toEqual("GET");
expect(req.request.params.get("courseId")).toEqual("12");
expect(req.request.params.get("filter")).toEqual("");
expect(req.request.params.get("sortOrder")).toEqual("asc");
expect(req.request.params.get("pageNumber")).toEqual("0");
expect(req.request.params.get("pageSize")).toEqual("3");
req.flush({
payload: findLessonsForCourse(12).slice(0, 3)
});
});
afterEach(() => {
// make sure the no extra http request are called
httpTestingController.verify();
});
});