fix: vars starting with 'mock' in hoisted context

[smbkr]

Summary

This PR attempts to address #3292, where variable whose name starts with mock cannot be used in a hoisted mock context.

In plain jest and jest+babel, one can reference a variable that is not yet initialised when creating a mock which jest will hoist by starting the name with mock, e.g. mockMyFoo. Presently this throws a ReferenceError when using ts-jest.

Test plan

So far I've added an e2e test that demonstrates this bug.

Does this PR introduce a breaking change?

• Yes
• No

Other information

[smbkr]

Opening this as a draft as I'd like to help here, but unsure how to proceed. So far, I've written a failing e2e test to demonstrate this bug.

Initially I started looking at src/transformers/hoist-jest.ts after some guidance from @ahnpnl on the open issue, however the test src/transformers/hoist-jest.spec.ts already checks that variables starting with mock are not causing issues when transforming due to being out of scope. See lines 151:153.

[ahnpnl]

The unit test data was wrong for MockMethods. It is just a constant and we didn’t put any jest.mock which uses that constant. We copied the test data from Jest which misses this line https://github.com/facebook/jest/blob/777e32687775b9287650c85ade4f9fdda1405fe1/e2e/babel-plugin-jest-hoist/__tests__/integration.test.js#L79

Also e2e test data we reuse the same test data Jest has to keep consistency. If you update e2e test, you should take from this https://github.com/facebook/jest/blob/main/e2e/babel-plugin-jest-hoist/__tests__/integration.test.js

if I’m not wrong in e2e we have copy 1-1 from jest for test data.

[ahnpnl]

There is one solution I can think of is: including the variables starting with mock into the list of statements to sort, see this

ts-jest/src/transformers/hoist-jest.ts

Line 86 in 45a3914

const sortStatements = (statements: _ts.Statement[]): _ts.Statement[] => {

If we do that way, we can ensure those variables will be always above jest.mock. The normal order for this case would be:

• variables starting with mock comes from import statement
• jest mock stuffs
• import or require statements

However, if those constants come from import or require statements, we need to ensure a different order:

• jest mock other stuffs
• import or require statements
• variables starting with mock comes from import or require statements
• jest mock apis

[smbkr]

Thanks @ahnpnl, I'm planning to continue looking at this when time permits