test: fix FlatESLint tests for caching

[mdjermanovic]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request? (put an "X" next to an item)

[ ] Documentation update
[ ] Bug fix (template)
[ ] New rule (template)
[ ] Changes an existing rule (template)
[ ] Add autofix to a rule
[ ] Add a CLI option
[ ] Add something to the core
[x] Other, please explain:

Fixes FlatESLint tests for caching.

I noticed that some flat-eslint tests for caching were failing when run directly, in a clean clone of the repo.

To reproduce locally:

rm -r tmp
node node_modules/mocha/bin/_mocha tests/lib/eslint/flat-eslint.js

 1) FlatESLint
       lintFiles()
         cache
           should create the cache file inside the provided directory using the cacheLocation option:

      AssertionError [ERR_ASSERTION]: the cache for eslint was created
      + expected - actual

      -false
      +true

      at Context.<anonymous> (tests\lib\eslint\flat-eslint.js:2309:17)

  2) FlatESLint
       lintFiles()
         cache
           when the cacheFile is a directory or looks like a directory
             should create the cache file inside the provided directory:

      AssertionError [ERR_ASSERTION]: the cache for eslint was created
      + expected - actual

      -false
      +true

      at Context.<anonymous> (tests\lib\eslint\flat-eslint.js:2282:21)

This means these tests were passing with npm test only because of the side effects of previously run tests for the ESLint class.

What changes did you make? (Give an overview)

Fixed those two tests, verified all flat-eslint tests for caching and fixed some more tests. Please see the review comments on the code. In addition to fixing/clarifying the tests, for each test for caching:

• I added a check to ensure that the cache file with which the test will work does not already exist.
• Updated error messages that were describing the expected result as if it actually happened. I believe this is not common, and when tests fail such messages are very confusing. I updated messages to either describe the actual unexpected result or the expected result but with "should" implying that it didn't happen.

Is there anything you'd like reviewers to focus on?

If this looks good, after merging I'll submit another PR to fix/sync tests in tests/lib/eslint/eslint.js as well.

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[mdjermanovic]

This was actually deleting nothing because the cache file is not named ".cache_hashOfCurrentWorkingDirectory". When this test was added in b5e66da, this was really deleting the cache file because the hash function was mocked in the tests, but that code disappeared over time.

I updated this to remove the .cacheFileDir/ directory as the name of this function suggests, since that makes the most sense for the tests.

[mdjermanovic]

This test was failing because it lints a file in a temporary directory, which is outside of the default cwd (project root) and is therefore considered ignored. Thus, this test wasn't actually creating the cache file. With npm test, the assertion was finding a cache file that was left from running tests/lib/eslint/eslint.js before.

I fixed this test and added two more tests in this group, so now we'll have 3 tests where cacheLocation is a directory:

1. The directory doesn't already exist but cacheLocation has a trailing slash so it looks like directory and thus FlatESLint creates the directory and the cache file inside it.
2. The directory already exists and cacheLocation has a trailing slash. FlatESLint uses the existing directory and creates the cache file inside it.
3. The directory already exists and cacheLocation doesn't have a trailing slash. FlatESLint finds that the path is a directory and therefore creates the cache file inside it.

[mdjermanovic]

This is the other failing test. This test was actually identical to the previous one, so I just deleted it. In the original commit b5e66da, one test was testing the cacheFile option of the CLIEngine constructor, the other was testing the cacheLocation option of the CLIEngine constructor. ESLint/FlatESLint constructors only have the cacheLocation option. While copying the tests from CLIEngine to ESLint, the cacheFile test was probably updated by mistake instead of just being deleted.

[mdjermanovic]

The old description does not at all match what this test is doing. It was probably a copy & paste error.

(original commit 9d4f4e4)

[mdjermanovic]

This test wasn't working as intended because cache[toBeDeletedFile] is undefined even if the file wasn't deleted.

[mdjermanovic]

Not sure why this was nested in another describe, seems unnecessary.

[nzakas]

LGTM. thanks for doing this.

I knew there were a lot hairy tests buried in the CLIEngine tests that I did my best to port over. I originally found a lot of tests that couldn't be run on their own so I'm not surprised there were more lurking.