Having trouble running tests on Angular service that has a Console constructor parameter

Question

Having trouble running tests on Angular service that has a Console constructor parameter

Attempting to incorporate a logging service in my project, the name service implies its purpose. During initialization, a specific implementation of the logging service is selected. This implementation utilizes the console for logging messages. Ensuring that the Console in the constructor is mockable without impacting the global console object is crucial.

Tests run successfully on Jasmine and the application functions properly, indicating a potential issue with Jest or its settings.

The goal is to inject the Console interface into an Angular service like so:

export class ConsoleLoggerService implements LoggerService {
   constructor(public console: Console) { }
}

During test execution:

describe('ConsoleLoggerService', () => {
  let service: ConsoleLoggerService;
  let consoleMock: Console;

  beforeEach(async(() => {
    consoleMock = {
      log(message?: any, ...optionalParams: any[]) { }
    } as Console;
    service = new ConsoleLoggerService(consoleMock);
  }));
  it('should be created', () => {
    expect(service).toBeTruthy();
  });
});

Encountering this error:

  ● Test suite failed to run

    ReferenceError: Console is not defined

       9 | export class ConsoleLoggerService implements LoggerService {
      10 |
    > 11 |   constructor(public console: Console) { }
         |                               ^

Considering that the Console interface should be globally accessible from @types/node, why does the test fail?

My development setup includes Angular 9, Jest 24.9, and Nx 9 in the workspace.

angular typescript jestjs

Answer 1

Answer №1

To verify if the console log function was called, you can utilize jest to mock it during testing. Within your test scenario, you may implement the following code snippet:

it('should console.log the text "hello"', () => {
  console.log = jest.fn();

  // Invoke a function that triggers the console logging

  // Check if the first call to console.log had the argument 'hello'
  expect(console.log.mock.calls[0][0]).toBe('hello');
});

For testing purposes, it is advisable to mock the console log function using jest as demonstrated above.

If you have a requirement to manually inject the console.log function, you can utilize TestBed to provide a simulated provider:

beforeEach(() => {
    TestBed.configureTestingModule({
        // MockConsole could be a custom fake class you define
        providers: [{provide: Console, useClass: MockConsole }]
    });
    service = TestBed.get(ConsoleLoggerService);
});

Answer 2

To verify if the console log function was called, you can utilize jest to mock it during testing. Within your test scenario, you may implement the following code snippet:

it('should console.log the text "hello"', () => {
  console.log = jest.fn();

  // Invoke a function that triggers the console logging

  // Check if the first call to console.log had the argument 'hello'
  expect(console.log.mock.calls[0][0]).toBe('hello');
});

For testing purposes, it is advisable to mock the console log function using jest as demonstrated above.

If you have a requirement to manually inject the console.log function, you can utilize TestBed to provide a simulated provider:

beforeEach(() => {
    TestBed.configureTestingModule({
        // MockConsole could be a custom fake class you define
        providers: [{provide: Console, useClass: MockConsole }]
    });
    service = TestBed.get(ConsoleLoggerService);
});

Having trouble running tests on Angular service that has a Console constructor parameter

Answer №1

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