I've been trying to unit test the subscribe function of this service. And looking at the code coverage report generated by istanbul, I can see that this code is not covered.

Code

layout.component.ts

import Component, HostListener, Input from '@angular/core';

import LayoutService from './layout.service';

import some from 'lodash';

@Component(
 selector: 'cgm-layout',
 templateUrl: './layout.component.html',
 styleUrls: ['./layout.component.scss'],
 providers: [LayoutService]
)
class LayoutComponent 

 message: any;

 constructor(
 private service: LayoutService
 ) 
 service.messagePublished$.subscribe(
 message => 
 this.setMessage(message);
 
 );
 

 setMessage(message): void 
 this.message = message;
 setTimeout(() => 
 this.message = null;
 , 7000);
 



export 
 LayoutComponent
;

This is my Unit Test

layout.component.spec.ts

import CUSTOM_ELEMENTS_SCHEMA, NO_ERRORS_SCHEMA from '@angular/core';
import async, ComponentFixture, fakeAsync, TestBed, tick from '@angular/core/testing';
import of from 'rxjs';
import LayoutComponent from './layout.component';
import LayoutService from './layout.service';

describe('LayoutComponent', () => 
 let component: LayoutComponent;
 let fixture: ComponentFixture<LayoutComponent>;
 let service;

 beforeEach(async(() => 
 service = new LayoutService();
 mockLayoutService = jasmine.createSpyObj('LayoutService', ['messagePublished$']);
 TestBed.configureTestingModule(
 declarations: [
 LayoutComponent,

 ],
 providers: [
 LayoutService
 ],
 schemas: [
 NO_ERRORS_SCHEMA, CUSTOM_ELEMENTS_SCHEMA
 ]
 )
 .compileComponents();
 ));

 beforeEach(() => 
 fixture = TestBed.createComponent(LayoutComponent);
 component = fixture.componentInstance;
 fixture.detectChanges();

 component.message = 'Garbage';
 );

 it('should call messagePublished', () => 
 spyOn(service.messagePublished$, 'subscribe');
 TestBed.createComponent(LayoutComponent);

 expect(service.messagePublished$.subscribe).toHaveBeenCalled();
 );

 describe('setMessage', () => 

 it('should set the Message', fakeAsync(() => 
 component.setMessage('Message');

 expect(component.message).toBe('Message');
 tick(7000);
 expect(component.message).toBeNull();
 ));

 );
);

So the code never seems to go over the 'service.messagePublished$.subscribe' part. Here is the code coverage report.

The error I'm getting is 'Expected spy subscribe to have been called', which I'm guessing is the error you get when that code block is not covered.

I'd advise you to move your subscription from the constructor to an ngOnInit. Angular created several lifecycle hooks which get called when a component get's created (ngOnInit) and other when data changes or when it gets destroyed - see Angular lifecycle hooks.

This way you can test your code by calling the ngOnInit() method.

In case you cannot change the code you can try creating a component instance and check if your method was called like in pseudo-code below:

import CUSTOM_ELEMENTS_SCHEMA, NO_ERRORS_SCHEMA from '@angular/core';
import async, ComponentFixture, fakeAsync, TestBed, tick from '@angular/core/testing';
import of from 'rxjs';
import LayoutComponent from './layout.component';
import LayoutService from './layout.service';

describe('LayoutComponent', () => 
 let component: LayoutComponent;
 let fixture: ComponentFixture<LayoutComponent>;
 let serviceSpy: jasmine.SpyObj<LayoutService>;;

 beforeEach(async(() => 
 const spy = spyOn(service.messagePublished$, 'subscribe')
 TestBed.configureTestingModule(
 declarations: [
 LayoutComponent,

 ],
 providers: [
 provide: LayoutService, useValue: spy 
 ],
 schemas: [
 NO_ERRORS_SCHEMA, CUSTOM_ELEMENTS_SCHEMA
 ]
 )
 .compileComponents();
 serviceSpy = TestBed.get(ValueService);
 ));

 beforeEach(() => 
 fixture = TestBed.createComponent(LayoutComponent);
 component = fixture.componentInstance;
 fixture.detectChanges();

 component.message = 'Garbage';
 );

 it('should call messagePublished', () => 
 TestBed.createComponent(LayoutComponent);

 expect(service.messagePublished$.subscribe).toHaveBeenCalled();
 );

);