refactor(utils): deprecate mocked util function (#3102)

Author: ahnpnl

.github/workflows/ci.yml

@@ -78,6 +78,7 @@ jobs:
         run: npm run test -- --coverage && cat ./coverage/lcov.info
         env:
           CI: true
+          DISABLE_MOCKED_WARNING: true
       - name: Coveralls parallel
         uses: coverallsapp/github-action@master
         with:

src/utils/testing.ts

@@ -1,3 +1,12 @@
+if (!process.env.DISABLE_MOCKED_WARNING) {
+  console.warn(
+    '\n`mocked` util function is now deprecated and has been moved to Jest repository,' +
+      ' see https://github.com/facebook/jest/pull/12089. In `ts-jest` v28.0.0, `mocked` function will be completely removed.' +
+      ' Users are encouraged to use to Jest v27.4.0 or above to have `mocked` function available from `jest-mock`. ' +
+      'One can disable this warning by setting environment variable process.env.DISABLE_MOCKED_WARNING=true\n',
+  )
+}
+
 // eslint-disable-next-line @typescript-eslint/no-explicit-any
 export type MockableFunction = (...args: any[]) => any
 export type MethodKeysOf<T> = { [K in keyof T]: T[K] extends MockableFunction ? K : never }[keyof T]