example.spec.ts

async function getUser(httpClient: HttpClient, userId: number): Promise<User> {
  const res = await httpClient.get(`/api/users/${userId}`)
  return res.data.user
}

describe('when the API ends in successful', () => {
  it('returns the user data', async () => {
    const get = jest.fn(() => {
      return Promise.resolve({
        data: {
          user: {
            id: 1,
            name: 'zochang'
          }
        }
      })
    })
    const dummyHttpClient = { get }
    const user = await getUser(dummyHttpClient, 1)
    expect(get).toHaveBeenCalledWith('/api/users/1')
    expect(user.name).toEqual('zochang')
  })
})