Encountering Angular error when trying to assign an undefined array to another array while using mock data

Attempting to conduct unit testing on a component involving the retrieval of 'Groups' data through a data resolver class. Below is the corresponding code:

export class GroupsComponent implements OnInit, OnDestroy {
  group: IGroup;
  groups: IGroup[];

  constructor(
    private activatedRoute: ActivatedRoute,
    private titleService: Title,
    private userService: GroupsService
  ){
     this.titleService.setTitle('Home | Groups');
     this.groups = [];

     this.groupsComponentDataSubscription = this.activatedRoute
        .data
        .subscribe(
       data => {

        if(data['groupsResponse']){
           this.groupsResponse = data['groupsResponse'] as IGroupsResponse;
           this.groups = this.groupsResponse.groups;
       }
      })
    }
  }

For testing purposes, using mock data for 'groupsResponse' as illustrated below:


let mockGroups: IGroup[] = [{
  groupName: "testGroup1",
  description : "group1 detail",
  apiRoles: ["foo", "bar", "monitoring"],
  kafkaClusters: [{
     clusterId: "cluster1",
     topics: ["foo", "bar"],
     connectClusters:[{
       clusteId: "testCluster1",
       connectorNames: ["foo", "bar"]
     }]
  }]
 },
groupName: "testGroup2",
  description : "group2 detail",
  apiRoles: ["foo", "bar", "foobar"],
  kafkaClusters: [{
     clusterId: "cluster2",
     topics: ["foo", "bar"],
     connectClusters:[{
       clusteId: "testCluster2",
       connectorNames: ["foo", "bar"]
     }]
  }]
 }
]

let mockGroupsResponse: IGroupsResponse = {
   groups: mockGroups
}

Subsequently, the mock value is passed for ActivatedRoute as shown:

let activatedRouteMock: any;

beforeEach(waitForAsync(() => {

activatedRouteMock = {
  data: of({groupsResponse: [mockGroupsResponse]})
};

TestBed.configureTestingModule({
 imports:[...],
 declarations: [GroupsComponent],
 providers:[..., {provide: ActivatedRoute, useValue: activatedRouteMock }]
}).compileComponents

Though the mock data for resolver is successfully read, the issue arises when attempting to assign the groups array from the response to the local variable.

constructor(
    private activatedRoute: ActivatedRoute,
    private titleService: Title,
    private userService: GroupsService
  ){
           ...
           ....
           this.groupsResponse = data['groupsResponse'] as IGroupsResponse; // groupsResponse is assigned as mock data -- console.log -> [{ groups: [object], [object]]
           this.groups = this.groupsResponse.groups; // encountered difficulty setting this.groups array from groupsResponse. (undefined)
       }
      })
    }
  }

Seeking insights on potential errors within the mock setup. While situations involving data retrieved from the resolver using http as Promise function smoothly, the test scenario proves to be problematic.

Answer №1

Restructures the code by transferring API calls from the constructor to the ngOnInit method.

The constructor is reserved for dependency injection purposes only. Source It's important to note that the constructor is executed before mock services are fully initialized.

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