@fetch-mock/codemods

A tool for helping upgrade to fetch-mock@12.

Usage

1. Install npm i -D @fetch-mock/codemods jscodeshift fetch-mock@12;
2. Manually modify any code using .sandbox() according to the example at the bottom of this page.
3. Run jscodeshift -t node_modules/@fetch-mock/codemods/src/index.js --ignore-pattern="node_modules/**/*" . to run over your entire project, or replace . with the directory/file paths you wish to modify. The jscodeshift CLI has many options - adjust them to suit your project. Note that the parser option should not be used as @fetch-mock/codemods forces use of the TSX parser in order to ensure compatibility with teh greatest range of projects.
4. For scenarios where the codemod is unable to detect which variable contains a fetch-mock instance (e.g. when it is required in a global set up file, or when using jest.mock() or fetch-mock-jest) you may pass in one or more variable names using the FM_VARIABLES environment variable e.g. FM_VARIABLES=fm,fetch
5. After the codemods have executed: a) If mocking global fetch you will probably need to add a call to .mockGlobal() at least once per test suite, possibly in a beforeAll/beforeEach block. b) Correct all the errors inserted by the codemod related to use of fallbackToNetwork, .calls() or .lastCall() usage. c) Run all your tests and fix any issues. If you believe the codemods have made any errors, or have missed any easy to modify patterns, please raise an issue.
6. Once all your tests are fixed you should be able to uninstall the codemods: npm uninstall @fetch-mock/codemods jscodeshift

Usage with fetch-mock-jest

If you're using fetch-mock-jest, you should migrate to @fetch-mock/jest, which is built around fetch-mock@12. While these codemods have not been tested on fetch-mock-jest, in principle you should be able use them by making similar adjustments to those described below about use with the sandbox() method, and by using the FM_VARIABLES environment variable to help the codemod identify which variables contain instances of fetch-mock.

Modifications that will be made

For everyt variable containing an instance of fetch-mock imported using require or import it will:

• Rewrite .mock() to .route()
• Rewrite .reset(), .restore(), .resetBehavior() and .resetHistory() to their equivalents in fetch-mock@12
• Rewrite .lastUrl(), .lastOptions() and lastResponse() to their equivalents in fetch-mock@12
• Adds an informative error whenever .lastCall() or .calls() are used with advice on how to manually correct these
• Converts .getOnce(), .getAnyOnce(), .postOnce() etc... - which have been removed - to calls to the underlying .get() method with additional options passed in.
• Removes uses of the deprecated options overwriteRoutes, warnOnFallback, sendAsJson
• Removes uses of the deprecated fallbackToNetwork option, and adds an informative error with details of how to replace with the spyGlobal() method

Limitations/Out of scope

• Javascript is a language with multiple ways to do the same thing. While these codemods attempt to cover a few different patterns, it's likely that they don't cover all the ways fetch-mock is being used. Please raise an issue if you think they can be improved.
• fetch-mock@12 no longer has the .mock() method which combines defining a route and setting up global mocking. All calls to .mock() are replaced by .route(). If using global fetch you will also need to call .mockGlobal() at least once per test suite.
• The .sandbox() method previously created a fetch function that also had all the fetch-mock methods attached. This is no longer the case, but pulling it apart is complex and deliberately left out of scope for this codemod.
• Any uses of fetch-mock prior to assigning to a variable will not be modified e.g. require('fetch-mock').mock('a', 'b') will not be converted to require('fetch-mock').route('a', 'b')
• When using a pattern such as jest.mock('node-fetch', () => require('fetch-mock').sandbox()), the codemod is unable to identify that require('node-fetch') will be an instance of fetch-mock.
• On the server side fetch-mock was previously built around node-fetch's classes, but now uses native fetch. In most cases, even if your application code still uses node-fetch, your mocks will still work. However, if you explicitly create instances of Request or Headers using node-fetch's classes, you may need to provide these to fetch-mock.

Manual adjustments when working with sandbox()

Taking the last 4 points together, this example illustrates the kind of manual modifications required:

Before

jest.mock('node-fetch', () => require('fetch-mock').sandbox());

const nodeFetch = require('node-fetch');

it('runs a test', () => {
	nodeFetch.get('http://a.com', 200);
	myAPI.call();
	expect(nodeFetch.called()).toBe(true);
});

After

const fetchMock = require('fetch-mock');

jest.mock('node-fetch', () => {
	const nodeFetch = jest.requireActual('node-fetch');
	// only needed if your application makes use of Response, Request
	// or Headers classes directly
	Object.assign(fetchMock.config, {
		fetch: nodeFetch,
		Response: nodeFetch.Response,
		Request: nodeFetch.Request,
		Headers: nodeFetch.Headers,
	});
	return fetchMock.fetchHandler;
});
const nodeFetch = require('node-fetch');

it('runs a test', () => {
	fetchMock.get('http://a.com', 200);
	myAPI.call();
	expect(fetchMock.called()).toBe(true);
});