docs: start documenting usage of codemods

packages/codemods/README.md

@@ -0,0 +1,61 @@
+# @fetch-mock/codemods
+
+A tool for helping upgrade to fetch-mock@12.
+
+## Features
+
+- Identifies instances of fetch-mock imported using `require` or `import`
+- Rewrites `.mock()` to `.route()`
+- Rewrites `.reset()`, `.restore()`, `.resetBehavior()` and `.resetHistory()` to their equivalents in fetch-mock@12
+- Rewrites `.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 thsi codemod.
+- Any uses of fetch-mock prior to assignig 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.
+
+Taking the last 3 points together, this example illustrates the kind of manual modifications required:
+
+### Before
+
+```js
+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
+
+```js
+const fetchMock = require('fetch-mock');
+
+jest.mock('node-fetch', () => fetchMock.fetchHandler);
+const nodeFetch = require('node-fetch');
+
+it('runs a test', () => {
+	fetchMock.get('http://a.com', 200);
+	myAPI.call();
+	expect(fetchMock.called()).toBe(true);
+});
+```
+
+## Usage
+
+1. Do all your manual mods
+2. run
+3. correct all errors
+   If you use `.sandbox()` or other mocing libraries to assign fetch-mock to

packages/codemods/src/__test__/integration.test.js

@@ -1,2 +1,3 @@
 // won't rewrite similarly named methods such as jest.mock
 // allow passing in a name of a fm variable to treat as an extra fetch-mock
+// The error for calls() should actually spell out the CallLog interface

packages/codemods/src/__test__/method-codemods.test.js

@@ -120,7 +120,22 @@ fetchMock.unmockGlobal();`,
 			);
 		});
 	});
-
+	describe('warning about CallLog', () => {
+		it('lastCall()', () => {
+			expectCodemodResult(
+				'fetchMock.lastCall()',
+				`throw new Error("lastCall() now returns a CallLog object instead of an array. Refer to the documentation")
+fetchMock.lastCall()`,
+			);
+		});
+		it('calls()', () => {
+			expectCodemodResult(
+				'fetchMock.calls()',
+				`throw new Error("calls() now returns an array of CallLog objects instead of an array of arrays. Refer to the documentation")
+fetchMock.calls()`,
+			);
+		});
+	});
 	describe('converting lastUrl()', () => {
 		it('single .lastUrl()', () => {
 			expectCodemodResult(
@@ -144,23 +159,6 @@ fetchMock.unmockGlobal();`,
 		});
 	});
 
-	describe('warning about CallLog', () => {
-		it('lastCall()', () => {
-			expectCodemodResult(
-				'fetchMock.lastCall()',
-				`throw new Error("lastCall() now returns a CallLog object instead of an array. Refer to the documentation")
-fetchMock.lastCall()`,
-			);
-		});
-		it('calls()', () => {
-			expectCodemodResult(
-				'fetchMock.calls()',
-				`throw new Error("calls() now returns an array of CallLog objects instead of an array of arrays. Refer to the documentation")
-fetchMock.calls()`,
-			);
-		});
-	});
-
 	describe('converting lastOptions()', () => {
 		it('single .lastOptions()', () => {
 			expectCodemodResult(