Network errors

I will start from implementing the error handling for network errors in get-auth-token.ts module.

Unlike error responses, network errors will reject the fetch promise. This means that I can handle those errors in the catch callback attached to that promise:

const response = await fetch('https://api.example.com/auth', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
  },
  body: JSON.stringify(credentials),
}).catch((error) => {
  throw new Error('Authentication failed: network error', { cause: error })
})

🦉 I am setting the original error as the cause property of the consumer-facing error for debugging purposes.

Next, let's mock the network error in the test.

In the get-auth-token.test.ts, I will head to the new empty test case and add a runtime handler that will always respond with a network error:

test('handles network errors', async () => {
  server.use(
    http.post('https://api.example.com/auth', () => {
      return Response.error()
    }),
  )

  await expect(() =>
    getAuthToken({
      email: 'kody@epicweb.dev',
      password: 'supersecret123',
    }),
  ).rejects.toThrow('Authentication failed: network error')
})

With this request handler, any request to the POST https://api.example.com/auth endpoint within this test will result in a network error. Note that I'm not trying to make the responses input-dependent, and instead introducing behavior-driven test cases to provide clarity and isolation for the tested code.

Finally, I will add an assertion for the getAuthToken() promise to verify that it rejects with the correct error message:

await expect(() =>
  getAuthToken({
    email: 'kody@epicweb.dev',
    password: 'supersecret123',
  }),
).rejects.toThrow('Authentication failed: network error')

05. Network/04. Network errors (🏁 solution)

Network errors