Why Does My Mock Of My Api Return A 404 Error?

I use axios-mock-adapter to mock my API, it works correctly but on one mock it returns a 404 error and I cannot found why.

There is here the sandbox with test, you can see when we run the test, the second check failed because the axios POST call haven't be mock. I have try to remove the header part but the sandbox has just crash when I have run test.

Mock of API (test part):

import axios from "axios";
import MockAdapter from 'axios-mock-adapter';
import Utils from "../Utils/Utils";

// Global variable for post request with axios
global.users_post = axios.create({
  baseURL: "http://localhost:5000/api/",
  headers: {'Content-Type': 'application/json'}

/* Mockup API */
var userMock = new MockAdapter(users_post);

const user_resp_full = {
  data: {
    first_name: "Test",
    last_name: "Test",
    email: "[email protected]",
    address: "Test",
    zipcode: 1010,
    city: "Test",
    admin: false

const testAPI = () => {
      .onPost("users", user_resp_full, Utils.getAuth())
      .reply(200, {data: {status: "success"}});

test("something", async () => {
  let tree = shallow(<UserManage type="create" uuid="" />);
  await flushPromises();
  // Some test

  await flushPromises();
  // Error 404, mock isn't trigger

I have already check, data is the same, same for endpoint but it seems doesn't mock it correctly.

Axios call in class:

function (fields) {"users", fields, Utils.getAuth())
    .then(resp => {
      let data =;
      // Do something
    .catch(resp => {
      let data =;
      // Display error

At this point, in my Jest test it returns a 404 error, so it hasn't mock my endpoint API (Other works).
The Utils.getAuth() function returns a header with a auth token.

Data send

That concerns content of data send (First is before the test call with mock, second is in the tested function and data log is the data send to api):

console.log src/tests/UserManage.test.js:222
{"first_name":"Test","last_name":"Test","email":"[email protected]","address":"Test","zipcode":1010,"city":"Test","admin":false}
console.log src/Components/Users/UserManage.js:152
console.log src/Components/Users/UserManage.js:153
{"first_name":"Test","last_name":"Test","email":"[email protected]","address":"Test","zipcode":1010,"city":"Test","admin":false}


This error happen only when I use a POST request with a header like that:"http://localhost/api/user/update", {name: "Test"}, {headers: {"Authorization": "Bearer token")}});

I have see on axios-mock-adapter github test page that eventually we should put headers in test without the label before:
{headers: {Autorization: "Bearer token"}} become {Autorization: "Bearer token"}
But unfortunately it doesn't work better than I have.


With the response of Matt Carlotta and his codesandbox, I modify mine with 2 examples of fixed issue:

  • A test of POST request mock using axios*
  • A test of POST request mock using an instance of axios*

* With axios-mock-adapter



Alrighty, round two.

  • Your flushPromises function isn't resolving promises properly when that promise takes some time to respond. The workaround is to return the promise and stick an await in front of it within the .test.js file. Since we're using await on the promise, await flushPromises() isn't needed.
  • In addition, including the headers within the onPost mocked function will cause the function to throw an error. Since you're just mocking this request (and not actually testing its integration), you don't need to include them. However, since you're already using a custom axios configuration anyway, you can just include the headers in the axiosConfig.js file. See the working example of your codesandbox for more information.

As demonstrated in the Unit Testing codesandbox below, if you try to use await flushPromises() on the deleteUserDataOverTime method, it fails. It fails because it didn't resolve the promise. This promise takes some time to resolve and isn't being handled properly.

In addition, due to the asynchronous nature of the tests, you shouldn't include unit and integration tests within the same test file. Since the tests are asynchronous, calling mockAxios.reset() or mockAxios.restore() on the same mocked request or same mocked instance -- to make any additional real or fake API calls -- can and will inadvertently impact all the API calls (again they're asynchronous, not synchronous tests).

Working example of Unit testing an API: (fake API -- includes GET, PUT, POST and DELETE)

Working example of Integration testing an API: (real API -- only includes GET, but functionality should remain the same for PUT, POST, and DELETE)

Working example of your codesandbox: