Testing - Can't resolve all parameters for (ClassName)

Question

Context

I created an ApiService class to be able to handle our custom API queries, while using our own serializer + other features.

ApiService's constructor signature is:

constructor(metaManager: MetaManager, connector: ApiConnectorService, eventDispatcher: EventDispatcher);

• MetaManager is an injectable service that handles api's metadatas.
• ApiConnectorService is a service which is wrapping Http to add our custom headers and signature system.
• EventDispatcher is basically Symfony's event dispatcher system, in typescript.

Problem

When I test the ApiService, I do an initialization in beforeEach:

beforeEach(async(() => {
    TestBed.configureTestingModule({
        imports  : [
            HttpModule
        ],
        providers: [
            ApiConnectorService,
            ApiService,
            MetaManager,
            EventDispatcher,
            OFF_LOGGER_PROVIDERS
        ]
    });
}));

and it works fine.

Then I add my second spec file, which is for ApiConnectorService, with this beforeEach:

beforeEach(async(() => {
    TestBed.configureTestingModule({
        imports  : [HttpModule],
        providers: [
            ApiConnectorService,
            OFF_LOGGER_PROVIDERS,
            AuthenticationManager,
            EventDispatcher
        ]
    });
}));

And all the tests fail with this error:

Error: Can't resolve all parameters for ApiService: (MetaManager, ?, EventDispatcher).

• If I remove api-connector-service.spec.ts (ApiConnectorService's spec file) from my loaded tests, ApiService's tests will succeed.
• If I remove api-service.spec.ts (ApiService's spec file) from my loaded tests, ApiConnectorService's tests will succeed.

Why do I have this error? It seems like the context between my two files are in conflict and I don't know why and how to fix this.

Answer 1

It's because the Http service can't be resolved from the HttpModule, in a test environment. It is dependent on the platform browser. You shouldn't even be trying to to make XHR calls anyway during the tests.

For this reason, Angular provides a MockBackend for the Http service to use. We use this mock backend to subscribe to connections in our tests, and we can mock the response when each connection is made.

Here is a short complete example you can work off of

import { Injectable } from '@angular/core';
import { async, inject, TestBed } from '@angular/core/testing';
import { MockBackend, MockConnection } from '@angular/http/testing';
import {
  Http, HttpModule, XHRBackend, ResponseOptions,
  Response, BaseRequestOptions
} from '@angular/http';

@Injectable()
class SomeService {
  constructor(private _http: Http) {}

  getSomething(url) {
	return this._http.get(url).map(res => res.text());
  }
}

describe('service: SomeService', () => {
  beforeEach(() => {
	TestBed.configureTestingModule({
	  providers: [
		{
		  provide: Http, useFactory: (backend, options) => {
			return new Http(backend, options);
		  },
		  deps: [MockBackend, BaseRequestOptions]
		},
		MockBackend,
		BaseRequestOptions,
		SomeService
	  ]
	});
  });

  it('should get value',
	async(inject([SomeService, MockBackend],
				 (service: SomeService, backend: MockBackend) => {

	backend.connections.subscribe((conn: MockConnection) => {
	  const options: ResponseOptions = new ResponseOptions({body: 'hello'});
	  conn.mockRespond(new Response(options));
	});

	service.getSomething('http://dummy.com').subscribe(res => {
	  console.log('subcription called');
	  expect(res).toEqual('hello');
	});
  })));
});

Answer 2

The issue wasn't really solved in the chosen answer, which is really just a recommendation for writing tests, but rather in the comments, and you have to follow a link and search for it there. Since I had another issue with the same error, I'll add both solutions here.

1. Solution to the OP's issue:

If you have a barrel (index.ts or multi export file) like this:

export * from 'my.component' // using my.service via DI
export * from 'my.service'

Then you could get an error like EXCEPTION: Can't resolve all parameters for MyComponent: (?).

To fix it, you have to export the service before the component:

export * from 'my.service'
export * from 'my.component' // using my.service via DI

2. Solution to my issue:

The same error can happen due to a circular dependency which causes an undefined service import. To check, console.log(YourService) after importing it (in your test file - where the issue is happening). If it's undefined, you may have made an index.ts file (barrel) exporting both the service and the file using it (component/effect/whatever you're testing) - by importing the service from the index file where both are exported (making it full circle).

Find that file and import the service you need directly from your.service.ts file instead of the index.