[FIXED] How to test public functions in Typescript with react-testing-library?

Issue

I'm having below setup in my project, whenever I extends the httpService and use the 'this.instance' in any service I'm getting the error.

If I use axios.get directly without any interceptors in my service files its working fine.

Im new to the unit testing and badly stuck with this. Please share your comments below. It'll be really helpful.

httpClient.ts

 import axios, { AxiosInstance, AxiosRequestConfig } from 'axios';
 import { DEFAULT_HEADERS, HOST } from './ApiHelper';
    
    export abstract class HttpService {
      protected readonly instance: AxiosInstance;
    
      public constructor(requestConfig: AxiosRequestConfig) {
        this.instance = axios.create(requestConfig);
    
        this.instance.interceptors.request.use((request) => {
          request.baseURL = HOST;
          request.headers = { ...DEFAULT_HEADERS };
          return request;
        });
    
        this.instance.interceptors.response.use(
          (response) =>
            response,
          (error) =>
            new Promise((resolve, reject) => {
              reject(error.response);
            }),
        );
      }
    }
    
    export default HttpService;

someService.ts

    import HttpService from './HttpService';
    
    const warningListUrl = 'some/url';
    
    class SomeService extends HttpService {
      public constructor() {
        super({
        });
      }
    
      public async getSomething(params: any) {
        this.instance({
          method: 'GET',
          url: warningListUrl,
          params,
        }).then((res) =>
          res.data);
      }
    }

export default SomeService;

ReactComponent.tsx

const fetchList = async () => {
    try {
      setIsLoading(true);
      const someService = new SomeService();
      const response: any = await someService.getSomething({});
      setWarnings(response.content);
      setTotalPages(response.totalPages);
    } catch (error) {
      console.log(error);
    } finally { setIsLoading(false); }
  };

  useEffect(() => {
    fetchList();
  }, []);

ReactComponent.test.tsx

jest.mock('../../services/SomeService');
const someService = new SomeService();


describe('page tests', () => {
  test('page renders without crashing', async () => {
    (someService.getWarningList as jest.Mock).mockResolvedValue(someMatchingData);
    await act(async () => {
      render(<ReactComponent />);
    });
    const text = screen.getByText('Warning 1');
    expect(text).toBeInTheDocument();
  });
}

Error:

TestingLibraryElementError: Unable to find an element with the text: Warning 1. This could be because the text is broken up by multiple elements. In this case, you can provide a function for your text matcher to make your matcher more flexible.

render(<Warning />);
});
-> const text = screen.getByText('Warning 1');
 expect(text).toBeInTheDocument();
});

Solution

Accessing methods through 'prototype' saved my day.

(someService.prototype.getWarningList as jest.Mock).mockResolvedValue(someMatchingData);

just adding it above the test description saved me.

Answered By - Ajithkumar S

Answer Checked By - Robin (PHPFixing Admin)