useDataApi.test.js

import React from "react";
import { useDataApi } from "path/to/hoo/useDataApi.jsx";
import "whatwg-fetch";
import { renderHook } from "@testing-library/react-hooks";
import fetchMock from "fetch-mock";
import { act } from "react-test-renderer";

describe("useDataApi", () => {
  beforeAll(() => {
    global.fetch = fetch;
  });
  afterAll(() => {
    fetchMock.restore();
  });

  it("should return data with a successful api request", async () => {
    const { result } = renderHook(() => useDataApi());
    
    // Tell the test that any request to 'test.com' should return 'returnedData: "foo"'
    fetchMock.mock("test.com", {
      returnedData: "foo"
    });
    
    // Calling the api via the `callApi` function
    await act(async () => {
      result.current.callApi("test.com");
    });
    
    // Check the 'data' state variable has the same mocked data from earlier
    expect(result.current.data).toBe({
      returnedData: "foo"
    });
  });
});