The error message "unit test undefined is not an object (evaluating 'this.groups.map')" indicates a problem with the mapping function

Question

The error message "unit test undefined is not an object (evaluating 'this.groups.map')" indicates a problem with the mapping function

Currently, I am working with this script:

  groups: Group[] = []

  constructor(

  ) {
    this.groups = AuthenticationService.getUserGroups()
    let menuList: any = []
    this.groups.map((permission: Group) => {
      menuList.push(...this.menuGenerator[permission.nomeGrupo.split('-')[1]])
    })
  }

However, when I execute npm run test, I encounter an error message stating

TypeError: undefined is not an object (evaluating 'this.groups.map')

. I am seeking the best solution to resolve this issue. I attempted using spyOn for getUserGroups, but it did not work. How can I assign a value to the variable in this case? Thank you for your assistance! This situation is crucial for my understanding!

javascript angular unit-testing typescript karma-jasmine

Answer 1

Answer №1

When employing a spy in your code, it takes over the function's role.

As a result, the function no longer returns anything.

This implies that you should initialize with:

groups = [];

After setting up the spy for your function:

spyOn(AuthenticationService, 'getUserGroups');

You will find:

groups = undefined;

To fix this issue, ensure that your spy returns a value:

spyOn(AuthenticationService, 'getUserGroups').and.returnValue([]);

UPDATE: Due to being in the constructor, spying on the component itself is not possible since it has not been created yet.

Fortunately, you can utilize prototypal inheritance to spy on the service prototype instead of the instance:

spyOn(AuthenticationService.prototype, 'getUserGroups').and.returnValue([]);

Add this right underneath describe('MyComponent') to execute it first.

Answer 2

When employing a spy in your code, it takes over the function's role.

As a result, the function no longer returns anything.

This implies that you should initialize with:

groups = [];

After setting up the spy for your function:

spyOn(AuthenticationService, 'getUserGroups');

You will find:

groups = undefined;

To fix this issue, ensure that your spy returns a value:

spyOn(AuthenticationService, 'getUserGroups').and.returnValue([]);

UPDATE: Due to being in the constructor, spying on the component itself is not possible since it has not been created yet.

Fortunately, you can utilize prototypal inheritance to spy on the service prototype instead of the instance:

spyOn(AuthenticationService.prototype, 'getUserGroups').and.returnValue([]);

Add this right underneath describe('MyComponent') to execute it first.

The error message "unit test undefined is not an object (evaluating 'this.groups.map')" indicates a problem with the mapping function

Answer №1

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