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Troubleshooting

The first step when debugging tests should be to run with the environment variable DEBUG=fetch-mock*. This will output additional logs for debugging purposes.

fetch is assigned to a local variable, not a global​

First of all, consider whether you could just use fetch as a global. Here are 3 reasons why this is a good idea:

  • The fetch standard defines it as a global (and in some cases it won't work unless bound to window), so to write isomorphic code it's probably best to stick to this pattern
  • isomorphic-fetch takes care of installing it as a global in Node.js or the browser, so there's no effort on your part to do so.
  • fetch-mock is primarily designed to work with fetch as a global and your experience of using it will be far more straightforward if you follow this pattern

Still not convinced?

In that case fetchMock.sandbox() can be used to generate a function which you can pass in to a mock loading library such as mockery instead of fetch

fetch doesn't seem to be getting mocked?​

  • If using a mock loading library such as mockery, are you requiring the module you're testing after registering fetch-mock with the mock loader? You probably should be (Example incorrect usage). If you're using ES6 import it may not be possible to do this without reverting to using require() sometimes.
  • If using isomorphic-fetch in your source, are you assigning it to a fetch variable? You shouldn't be i.e.
    • import 'isomorphic-fetch', not import fetch from 'isomorphic-fetch'
    • require('isomorphic-fetch'), not const fetch = require('isomorphic-fetch')

Environment doesn't support requiring fetch-mock?​

  • If your client-side code or tests do not use a loader that respects the browser field of package.json use require('fetch-mock/es5/client').
  • If you need to use fetch-mock without commonjs, you can include the precompiled node_modules/fetch-mock/es5/client-browserified.js in a script tag. This loads fetch-mock into the fetchMock global variable.
  • For server side tests running in Node.js 0.12 or lower use require('fetch-mock/es5/server')

Matching Request objects in node fails​

In node, if your Request object is not an instance of the Request constructor used by fetch-mock, you need to set a reference to your custom request class. This needs to be done if you are mocking the Request object for a test or you are running npm with a version below 3.

  • use fetchMock.config.Request = myRequest, where myRequest is a reference to the Request constructor used in your application code.

it.md

  • When using karma-webpack it's best not to use the webpack.ProvidePlugin for this. Instead just add node_modules/whatwg-fetch/fetch.js to your list of files to include, or require it directly into your tests before requiring fetch-mock.

  • chaining

  • note that end matches qs, path matches only path

Put this with the spy() docs When using node-fetch, fetch-mock will use the instance you have installed. The one exception is that a reference to fetchMock.config.fetch = require('node-fetch') is required if you intend to use the .spy() method)

to Within individual tests .catch() and spy() can be used for fine-grained control of this"