Error Handling in Unit Testing with Angular: Understanding the "Cannot Read Property * of Undefined" Issue in Karma

When it comes to Interfaces in Angular Karma Jasmine unit tests, I'm struggling with a specific error message. It's saying undefined for the first property of the interface and I can't get the component to run.

Cannot read property of 'primaryPropertyMailingAddressId' of undefined

Karma/Jasmine:

 beforeEach(async(() => {

    fixture = TestBed.createComponent(PropertySitusFinalizeComponent);
    component = fixture.componentInstance;

    component.jsonData = {};  // whether I remove or keep this line doesn't affect the error message

    fixture.detectChanges();

  }));

  it('should create', () => {
    expect(component).toBeTruthy();
  });

Component:

export class PropertySitusFinalizeComponent implements OnInit {

  @Input() jsonData: PropertySitusAddressContainer;

Interface:

export interface PropertySitusAddressContainer {
  queueItemId?: number;
  existingPropertySitusAddress?: PropertySitusAddress;  

export class PropertySitusAddress {

    primaryPropertyMailingAddressId?:number = null;
    propertyId?: number = null;
    propertySitusAddressId?: number = null;
    addressFormatId?: number = null; 
    apn?: string = null;

Resource:

How to unit test model interfaces in typescript?

Answer №1

Ensure to set up the initial values:

@Input() jsonData: PropertySitusAddressContainer = {
      existingPropertySitusAddress = {}
}

By doing this, all fields accessed using . operators must be initialized.

For your html, consider using

value = "jsonData?.existingPropertySitusAddress?.primaryPropertyMailingAddressId"
for better type safety.

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