Seeking the Origin of NgxMqttServiceConfig Import: Dealing with NullInjectorError in Angular Testing

Question

Seeking the Origin of NgxMqttServiceConfig Import: Dealing with NullInjectorError in Angular Testing

While working on an application using Angular 8 and ngx-mqtt, I encountered an error when running the tests defined in the .spec.ts files. The error message reads:

        NullInjectorError: StaticInjectorError(DynamicTestModule)[InjectionToken NgxMqttServiceConfig]: 
      StaticInjectorError(Platform: core)[InjectionToken NgxMqttServiceConfig]: 
        NullInjectorError: No provider for InjectionToken NgxMqttServiceConfig!
    error properties: Object({...})
        at <Jasmine>
        ...
        at ZoneDelegate.invoke (...)

The .spec.ts file I am currently using is as follows:

describe("MoviesComponent", () => {
    let component: MoviesComponent;
    let fixture: ComponentFixture<MoviesComponent>;

    TestBed.prepare([MoviesComponent]);

    beforeEach(() => {
        fixture = TestBed.createComponent(MoviesComponent);
        component = fixture.componentInstance;
        fixture.detectChanges();
    });

    it("should create", () => {
        expect(component).toBeTruthy();  // <------- FAILS HERE
    });
});

Within the .component.ts file, I utilize MqttService imported from "ngx-mqtt" and injected through the constructor. Although the components function correctly, the tests are failing. I have minimal experience with .spec.ts files, yet I suspect that the error could be related to a missing import or provider within the test file.

I attempted adding MqttServiceConfig to the MoviesComponent.spec.ts like so:

beforeEach(() => {
    fixture = TestBed.configureTestingModule({ imports: [MqttServiceConfig] }).createComponent(MoviesComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
});

Additionally, I tried this approach after referencing this tutorial:

it('should create', async(inject([MqttServiceConfig], (myService: MqttServiceConfig) => ...

My struggle lies in not knowing where to import NgxMqttServiceConfig from. It appears to be contained within MqttModule, yet it is not exposed. I also attempted using MqttModule instead of MqttServiceConfig, but to no avail. What am I overlooking?

angular typescript automated-tests karma-jasmine

Answer 1

Answer №1

After some trial and error, I discovered that the key to success was integrating MqttModule with its proper configuration into the TestBed within AppComponent. Initially, I mistakenly attempted to add MqttModule by itself and in MoviesComponent instead of AppComponent.

Here is a snippet from my app.module.ts:

@NgModule({
    declarations: [
        AppComponent,
        MoviesComponent,
        ...
    ],
    imports: [
        BrowserModule,
        HttpClientModule,
        MqttModule.forRoot(AppConstants.MQTT_SERVICE_OPTIONS),
        ...
    ],
    providers: [
        { provide: ErrorHandler, useClass: ErrorHandlerService },
        ...
    ],
    bootstrap: [
        AppComponent
    ]
})
export class AppModule { }

And from my app.component.spec.ts:

beforeEach(async(() => {
    TestBed.configureTestingModule({
        imports: [
            HttpClientModule,
            MqttModule.forRoot(AppConstants.MQTT_SERVICE_OPTIONS),
            ...
        ],
        providers: [
            { provide: ErrorHandler, useClass: ErrorHandlerService },
            ...
        ]
    }).compileComponents();
}));

In this setup,

AppConstants.MQTT_SERVICE_OPTIONS

serves as a plain object containing the necessary configuration for ngx-mqtt.

Answer 2

After some trial and error, I discovered that the key to success was integrating MqttModule with its proper configuration into the TestBed within AppComponent. Initially, I mistakenly attempted to add MqttModule by itself and in MoviesComponent instead of AppComponent.

Here is a snippet from my app.module.ts:

@NgModule({
    declarations: [
        AppComponent,
        MoviesComponent,
        ...
    ],
    imports: [
        BrowserModule,
        HttpClientModule,
        MqttModule.forRoot(AppConstants.MQTT_SERVICE_OPTIONS),
        ...
    ],
    providers: [
        { provide: ErrorHandler, useClass: ErrorHandlerService },
        ...
    ],
    bootstrap: [
        AppComponent
    ]
})
export class AppModule { }

And from my app.component.spec.ts:

beforeEach(async(() => {
    TestBed.configureTestingModule({
        imports: [
            HttpClientModule,
            MqttModule.forRoot(AppConstants.MQTT_SERVICE_OPTIONS),
            ...
        ],
        providers: [
            { provide: ErrorHandler, useClass: ErrorHandlerService },
            ...
        ]
    }).compileComponents();
}));

In this setup,

AppConstants.MQTT_SERVICE_OPTIONS

serves as a plain object containing the necessary configuration for ngx-mqtt.

Answer 3

Answer №2

To avoid encountering this issue, you can incorporate the following app.module.ts code:

import { NgModule } from '@angular/core'; 
import { MqttModule, MQTT_SERVICE_OPTIONS } from 'ngx-mqtt'; import { BrowserModule } from '@angular/platform-browser'; 
import { RouteReuseStrategy } from '@angular/router'; 
import { IonicModule, IonicRouteStrategy } from '@ionic/angular'; 
import { AppComponent } from './app.component'; 
import { AppRoutingModule } from './app-routing.module'; 
    
@NgModule({ 
    declarations: [AppComponent], 
    imports: [ 
        BrowserModule,
        IonicModule.forRoot(),
        AppRoutingModule,
        MqttModule.forRoot(MQTT_SERVICE_OPTIONS), 
    ], 
    providers: [
        { provide: RouteReuseStrategy, useClass: IonicRouteStrategy }
    ], 
    bootstrap: [AppComponent], }
)
    
export class AppModule {}

Answer 4

To avoid encountering this issue, you can incorporate the following app.module.ts code:

import { NgModule } from '@angular/core'; 
import { MqttModule, MQTT_SERVICE_OPTIONS } from 'ngx-mqtt'; import { BrowserModule } from '@angular/platform-browser'; 
import { RouteReuseStrategy } from '@angular/router'; 
import { IonicModule, IonicRouteStrategy } from '@ionic/angular'; 
import { AppComponent } from './app.component'; 
import { AppRoutingModule } from './app-routing.module'; 
    
@NgModule({ 
    declarations: [AppComponent], 
    imports: [ 
        BrowserModule,
        IonicModule.forRoot(),
        AppRoutingModule,
        MqttModule.forRoot(MQTT_SERVICE_OPTIONS), 
    ], 
    providers: [
        { provide: RouteReuseStrategy, useClass: IonicRouteStrategy }
    ], 
    bootstrap: [AppComponent], }
)
    
export class AppModule {}

Seeking the Origin of NgxMqttServiceConfig Import: Dealing with NullInjectorError in Angular Testing

Answer №1

Answer №2

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