Unit test error: Cannot call Promise.then from within a sync test

Question

I started looking into unit testing angular 2 applications, but I'm stuck even in the simplest examples. I just want to run a simple test to see if it even works, basically what I want is to compare a value from the title page to the one in the test.

This is the error I'm getting, but I don't see where the error is coming from since everything looks to be synchronous to me.

Error: Error: Cannot call Promise.then from within a sync test.

Unit test:

import { ComponentFixture, TestBed } from '@angular/core/testing';
import { By }              from '@angular/platform-browser';
import { DebugElement, Input}    from '@angular/core';
import { ToDoComponent } from './todo.component';
import { FormsModule } from '@angular/forms';
describe(("test input "),() => {
    let comp:    ToDoComponent;
    let fixture: ComponentFixture<ToDoComponent>;
    let de:      DebugElement;
    let el:      HTMLElement;

    beforeEach(() => {
        TestBed.configureTestingModule({
            declarations: [ ToDoComponent ],
            imports: [ FormsModule ]
        })
        .compileComponents();  
    });

    fixture = TestBed.createComponent(ToDoComponent);
    comp = fixture.componentInstance;
    de = fixture.debugElement.query(By.css("h1"));
    el = de.nativeElement;

    it('should display a different test title', () => {
        comp.pageTitle = 'Test Title';
        fixture.detectChanges();
        expect(el.textContent).toBe('Test Title423');
    });
});

My component:

import {Component} from "@angular/core";
import {Note} from "app/note";

@Component({
    selector : "toDoArea",
    templateUrl : "todo.component.html"
})

export class ToDoComponent{
    pageTitle : string = "Test";
    noteText : string ="";
    noteArray : Note[] = [];
    counter : number = 1;
    removeCount : number = 1;

    addNote() : void {

        if (this.noteText.length > 0){
            var a = this.noteText;
            var n1 : Note = new Note();
            n1.noteText = a;
            n1.noteId = this.counter;
            this.counter = this.counter + 1;
            this.noteText = "";
            this.noteArray.push(n1);        
        }

    }

    removeNote(selectedNote : Note) :void{
        this.noteArray.splice(this.noteArray.indexOf(selectedNote),this.removeCount);
    }

}

Answer 1

Move your variable initialization inside a beforeEach.

You shouldn't be getting things out of the TestBed or managing the fixture or component in the describe scope. You should only do these things within the scope of a test run: inside a beforeEach/beforeAll, afterEach/afterAll, or inside an it.

describe(("test input "), () => {
  let comp: ToDoComponent;
  let fixture: ComponentFixture<ToDoComponent>;
  let de: DebugElement;
  let el: HTMLElement;

  beforeEach(async(() => {
    TestBed.configureTestingModule({
        declarations: [ToDoComponent],
        imports: [FormsModule]
      })
      .compileComponents();
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(ToDoComponent);
    comp = fixture.componentInstance;
    de = fixture.debugElement.query(By.css("h1"));
    el = de.nativeElement;
  })


  it('should display a different test title', () => {
    comp.pageTitle = 'Test Title';
    fixture.detectChanges();
    expect(el.textContent).toBe('Test Title423');
  });

});

See also

• https://angular.io/docs/ts/latest/guide/testing.html#!#waiting-compile-components

Answer 2

I got the same error for a different reason. I put a TestBed.get(Dependency) call within a describe block. The fix was moving it to the it block.

Wrong:

describe('someFunction', () => {
    const dependency = TestBed.get(Dependency); // this was causing the error

    it('should not fail', () => {
        someFunction(dependency);
    });
});

Fixed:

describe('someFunction', () => {
    it('should not fail', () => {
        const dependency = TestBed.get(Dependency); // putting it here fixed the issue
        someFunction(dependency);
    });
});