The Elusive MatSnackBar: Debugging the “Open” Function Call

Are you tired of pulling your hair out trying to figure out why your MatSnackBar “Open” function isn’t being called during testing? You’re not alone! In this article, we’ll dive into the common pitfalls and misunderstandings surrounding this tricky issue, and provide you with a step-by-step guide to get your tests running smoothly.

Understanding the MatSnackBar “Open” Function

The MatSnackBar is an essential component in Angular Material, allowing developers to display snack bars with messages, actions, and other interactive elements. At its core, the MatSnackBar relies on the “Open” function to, well, open the snackbar. This function is responsible for rendering the snackbar content and animating its appearance.

import { MatSnackBar } from '@angular/material/snack-bar';

@Component({
  selector: 'app-example',
  template: 'Open SnackBar'
})
export class ExampleComponent {
  constructor(private snackBar: MatSnackBar) { }

  openSnackBar() {
    this.snackBar.open('Hello,SnackBar!');
  }
}

The Problem: “Expect MatSnackBar ‘Open’ function to be called” Fails

When writing unit tests for your component, you might encounter an issue where the “Open” function isn’t being called, despite your test expecting it to. This can be frustrating, especially when you’ve double-checked your code and ensured that the MatSnackBar is properly imported and configured.

import { TestBed, ComponentFixture } from '@angular/core/testing';
import { MatSnackBar } from '@angular/material/snack-bar';
import { ExampleComponent } from './example.component';

describe('ExampleComponent', () => {
  let component: ExampleComponent;
  let fixture: ComponentFixture;
  let snackBarSpy: jasmine.Spy;

  beforeEach(async () => {
    await TestBed.configureTestingModule({
      declarations: [ExampleComponent],
      providers: [{ provide: MatSnackBar, useValue: jasmine.createSpyObj('MatSnackBar', ['open']) }]
    }).compileComponents();
  });

  beforeEach(() => {
    fixture = TestBed.createComponent(ExampleComponent);
    component = fixture.componentInstance;
    snackBarSpy = TestBed.inject(MatSnackBar) as jasmine.Spy;
  });

  it('should call MatSnackBar open function', () => {
    component.openSnackBar();
    expect(snackBarSpy.open).toHaveBeenCalledTimes(1);
  });
});

Why It Fails: The Culprits

There are several reasons why your test might be failing to detect the “Open” function call. Let’s explore the most common culprits:

• Incorrect Import Order: Make sure you’re importing the MatSnackBar module after the Angular Material module. The correct order is:

import { BrowserAnimationsModule } from '@angular/platform-browser/animations';
import { MATERIAL_SANITY_CHECKS } from '@angular/material/core';
import { MatSnackBarModule } from '@angular/material/snack-bar';

• Misconfigured Providers: Ensure you’re providing the MatSnackBar correctly in your test bed configuration. Avoid using the actual MatSnackBar service, and instead, create a spy object:

providers: [{ provide: MatSnackBar, useValue: jasmine.createSpyObj('MatSnackBar', ['open']) }]>

• Forgot to Call fixture.detectChanges(): Don’t forget to call fixture.detectChanges() after triggering the snackbar opening. This ensures the component is fully rendered and the change detection cycle is completed:

it('should call MatSnackBar open function', () => {
  component.openSnackBar();
  fixture.detectChanges(); // Don't forget this!
  expect(snackBarSpy.open).toHaveBeenCalledTimes(1);
});

• Async Operations and Timing Issues: MatSnackBar operations might be asynchronous, which can lead to timing issues in your tests. Make sure to use async/await or the whenStable() method to ensure the snackbar is fully opened before making assertions:

it('should call MatSnackBar open function', async () => {
  component.openSnackBar();
  await fixture.whenStable();
  expect(snackBarSpy.open).toHaveBeenCalledTimes(1);
});

Solution: A Step-by-Step Guide

To avoid the common pitfalls and ensure your test detects the MatSnackBar “Open” function call, follow these steps:

1. Import the MatSnackBar module correctly:

import { MatSnackBarModule } from '@angular/material/snack-bar';

2. Create a spy object for the MatSnackBar service:

providers: [{ provide: MatSnackBar, useValue: jasmine.createSpyObj('MatSnackBar', ['open']) }]>

3. Trigger the snackbar opening in your component:

component.openSnackBar();

4. Call fixture.detectChanges() to ensure the component is fully rendered:

fixture.detectChanges();

5. Use async/await or the whenStable() method to wait for the snackbar to open:

await fixture.whenStable();

6. Make assertions about the MatSnackBar “Open” function call:

expect(snackBarSpy.open).toHaveBeenCalledTimes(1);

Conclusion

By following these steps and avoiding the common pitfalls, you should be able to write robust unit tests that accurately detect the MatSnackBar “Open” function call. Remember to import the MatSnackBar module correctly, create a spy object, trigger the snackbar opening, call fixture.detectChanges(), and use async/await or the whenStable() method to wait for the snackbar to open.

With these tips, you’ll be well on your way to writing reliable and efficient tests for your Angular Material applications. Happy testing!

Common Issues	Solutions
Incorrect Import Order	Import MatSnackBar module after Angular Material module
Misconfigured Providers	Use jasmine.createSpyObj for MatSnackBar
Forgot to Call fixture.detectChanges()	Call fixture.detectChanges() after triggering snackbar opening
Async Operations and Timing Issues	Use async/await or fixture.whenStable() to wait for snackbar to open

Frequently Asked Question

Stuck with MatSnackBar testing? We’ve got you covered! Here are some FAQs to help you debug the issue: