Error encountered in Angular with Karma and Jasmine: The function this.Service.<foo> is not defined in the Lifecycle Hook

Question

Error encountered in Angular with Karma and Jasmine: The function this.Service.<foo> is not defined in the Lifecycle Hook

When running Karma and Jasmine tests using the

npm run test -- --no-watch --no-progress

command with Karma/Jasmine, an error is thrown:

Chrome 92.0.4515.159 (Mac OS 10.15.7) LoginComponent should create FAILED
    TypeError: this.loggerService.onDebug is not a function
        at LoginComponent.ngAfterViewInit (src/app/pages/login/login.component.ts:22:24)
        ...

Greetings,

I am currently working on a Logger Service in Angular version 12.0.x that forwards log messages to both ngx-logger (e.g., an external server) and a store (ngxs).

The karma.conf.js file is located at the root of the application.

The Logger Service (logging-service.ts) is pretty straightforward:

import { Injectable } from '@angular/core';
...

@Injectable({
  providedIn: 'root',
})
export class LoggerService {
...

The Logger Service's methods are utilized in two different components:

Login Component
Log Manager Component

...

Any suggestions on how to approach this issue? :)

angular typescript jasmine karma-jasmine lifecycle

Answer 1

Answer №1

When using TestBed.configureTestingModule in a test, the

providers: [{ provide: LoggerService, useClass: class {} }]

part indicates that an empty object (represented by {}) should be provided as a mock object instead of the actual LoggerService. Since the empty object does not contain an onDebug function, the error

this.loggerService.onDebug is not a function

is thrown during the test execution. This error does not occur when running the application with ng serve, as the actual implementation of onDebug exists within the provided LoggerService.

Therefore, if you need to create a mock object for the LoggerService in your test, you must ensure that the necessary functions are mocked from the LoggerService itself. For instance, if only the onDebug function is required:

await TestBed.configureTestingModule({
  declarations: [LoginComponent],
  providers: [{ provide: LoggerService, useClass: LoggerServiceMock }],
}).compileComponents();

...

// Outside of the jasmine describes
class LoggerServiceMock {
  onDebug(origin: string, msg: string) {};
}

In this scenario, the onDebug function is now an empty function serving as an example. This empty function will be invoked in the tests instead of the original onDebug function of the LoggerService. Using such mock objects may not be necessary if the actual LoggerService is provided in the test and the required functions are overridden with Jasmine spies.

Answer 2

When using TestBed.configureTestingModule in a test, the

providers: [{ provide: LoggerService, useClass: class {} }]

part indicates that an empty object (represented by {}) should be provided as a mock object instead of the actual LoggerService. Since the empty object does not contain an onDebug function, the error

this.loggerService.onDebug is not a function

is thrown during the test execution. This error does not occur when running the application with ng serve, as the actual implementation of onDebug exists within the provided LoggerService.

Therefore, if you need to create a mock object for the LoggerService in your test, you must ensure that the necessary functions are mocked from the LoggerService itself. For instance, if only the onDebug function is required:

await TestBed.configureTestingModule({
  declarations: [LoginComponent],
  providers: [{ provide: LoggerService, useClass: LoggerServiceMock }],
}).compileComponents();

...

// Outside of the jasmine describes
class LoggerServiceMock {
  onDebug(origin: string, msg: string) {};
}

In this scenario, the onDebug function is now an empty function serving as an example. This empty function will be invoked in the tests instead of the original onDebug function of the LoggerService. Using such mock objects may not be necessary if the actual LoggerService is provided in the test and the required functions are overridden with Jasmine spies.

Answer 3

Answer №2

The reason your test may be failing is because you are using an empty class as a mock:

providers: [{ provide: LoggerService, useClass: class {} }]

This results in the error "onDebug is not a function."

One possible solution is to use useValue:

I recommend providing a mocked value (useValue:) that includes an onDebug function:

providers: [{ provide: LoggerService, useValue: { onDebug: (origin: string, msg: string) => undefined} }]

Another solution is to use useClass:

You can create a simple mock class for this purpose.

In your spec file:

class LoggerServiceMock {
    onDebug(origin: string, msg: string) { // do nothing }
}
...
...
providers: [{ provide: LoggerService, useClass: LoggerServiceMock }]

Answer 4

The reason your test may be failing is because you are using an empty class as a mock:

providers: [{ provide: LoggerService, useClass: class {} }]

This results in the error "onDebug is not a function."

One possible solution is to use useValue:

I recommend providing a mocked value (useValue:) that includes an onDebug function:

providers: [{ provide: LoggerService, useValue: { onDebug: (origin: string, msg: string) => undefined} }]

Another solution is to use useClass:

You can create a simple mock class for this purpose.

In your spec file:

class LoggerServiceMock {
    onDebug(origin: string, msg: string) { // do nothing }
}
...
...
providers: [{ provide: LoggerService, useClass: LoggerServiceMock }]

Error encountered in Angular with Karma and Jasmine: The function this.Service.<foo> is not defined in the Lifecycle Hook

Answer №1

Answer №2

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