No provider for MatSnackBar error when trying to run "ng test"

You should import the module instead of the component.

import { MatSnackBar, MatSnackBarModule } from '@angular/material';
....
describe('BranchNameCellComponent', () => {
  let component: BranchNameCellComponent;
  let fixture: ComponentFixture<BranchNameCellComponent>;
    
  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [ BranchNameCellComponent ],
      imports: [ HttpClientTestingModule, ReactiveFormsModule, MatSnackBarModule ],
      schemas: [ NO_ERRORS_SCHEMA ]
    }).compileComponents();
  }));
    
  it('should create', () => {
    fixture = TestBed.createComponent(BranchNameCellComponent);
    component = fixture.componentInstance;
    expect(component).toBeTruthy();
  });
});

For the issue related to the timeout, try adding this to your karma config file:

captureTimeout: 210000,
browserDisconnectTolerance: 3, 
browserDisconnectTimeout : 210000,
browserNoActivityTimeout : 210000,

This has happened to me recently and I decided like this::

Include file aap.module.ts

import { MatSnackBarModule } from '@angular/material/snack-bar';
...
...
imports: [
    ...
    MatSnackBarModule
  ]
...

On file component or service:

import { MatSnackBar } from '@angular/material/snack-bar';
...
...
constructor(private snackBar: MatSnackBar) { }
...

I was facing this error when in my angular app, I was navigating to some module which was lazy loaded. This module was importing MatSnackBarModule but I needed to import MatSnackBarModule in app.module.ts file as well