Mock ActivatedRoute (with snapshot, queryParams and params), tested in Angular 7+

mock-active-router.ts

import { Params } from '@angular/router';
import { BehaviorSubject } from 'rxjs';

export class MockActivatedRoute {
  private innerTestParams?: any;
  private subject?: BehaviorSubject<any> = new BehaviorSubject(this.testParams);

  params = this.subject.asObservable();
  queryParams = this.subject.asObservable();

  constructor(params?: Params) {
    if (params) {
      this.testParams = params;
    } else {
      this.testParams = {};
    }
  }

  get testParams() {
    return this.innerTestParams;
  }

  set testParams(params: {}) {
    this.innerTestParams = params;
    this.subject.next(params);
  }

  get snapshot() {
    return { params: this.testParams, queryParams: this.testParams };
  }
}

my-component.spec.ts

// details were omitted
// Import the mock class
import { MockActivatedRoute } from './mock-active-router';

describe('MyComponent', () => {
  let component: MyComponent;
  let fixture: ComponentFixture<MyComponent>;
  let activatedRouteStub: MockActivatedRoute;

  beforeEach(async(() => {
    activatedRouteStub = new MockActivatedRoute();
    TestBed.configureTestingModule({
      declarations: [MyComponent],
      providers: [
        { provide: ActivatedRoute, useValue: activatedRouteStub }
      ]
    }).compileComponents();
  }));

  it('should change params', () => {
    expect(component.myparam).toBeUndefined();
    expect(component.paramTwo).toBeUndefined();

    activatedRouteStub.testParams = {
      myparam: 'value',
      paramTwo: 1
    };
    fixture.detectChanges();

    expect(component.myparam).toEqual('value');
    expect(component.paramTwo).toEqual(1);
  });

You just ended my 3 hour descent into madness. Thank you <3