Fixes #2342 -- get_mimetype tests fail without file in PATH

[alzwded]

Description

In tests_file.lua, mock vim.fn.executable to yield 1 or 0 depending on what the test is trying to test.

Related Issue(s)

• Fixes [Bug]: get_mimetype tests fail without file in PATH #2342

Screenshots

Checklist

• I've read the contributing guidelines and have adhered to them in this PR
• I've added test coverage for this fix/feature
• I've run make all to ensure docs are generated, tests pass and my formatting is applied
• (optional) I've updated CodeCompanion.has in the init.lua file for my new feature
• (optional) I've updated the README and/or relevant docs pages

[olimorris]

It's early here but I don't understand this test

[alzwded]

I've only learnt about these two tests 30 minutes ago when I rebased to main :-P

Initially, I wanted to add MiniTest.skip, but then I realized it wasn't actually executing anything.

Going off the testcase descriptions, one tests that get_mimetype invokes the file executable with those arguments, and the other checks that if the file executable is not available, then it is supposed to return a mime type using a fallback-extension based-lookup table.

T["Files utils"]["get_mimetype"]["can invoke `file`"]
T["Files utils"]["get_mimetype"]["works without `file`"]

That's not what the tests were doing, though. This PR adds a mock for vim.fn.executable so that the test setup matches the testcase description.

The implementation in utils.files first checks if there is a file in path, and only calls vim.system if there is one.

I don't particularly care if you accept this PR, but the docs say file is optional, the implementation has a fallback, and the tests are failing if there is no file in PATH (which happens to be the default state on Windows)

[Davidyz]

@olimorris the new get_mimetype uses the file command to detect mimetype when it's available. The vim.system is mocked because I've had some weird experiences with path handling on GitHub Actions (tl;dr is there seems to be some symlinks that make paths weird and may break the tests for no reason).

Regarding this PR, I suggest the following changes:

1. In T["Files utils"]["get_mimetype"]["can invoke file"], we mock vim.fn.executable so that it returns 1 and triggers the (mocked) file command. This test makes sure the get_mimetype function can parse the output of the file command.
2. Rename T["Files utils"]["get_mimetype"]["works without file"] to T["Files utils"]["get_mimetype"]["works with fallback"], and mock vim.fn.executable to return 0 so that it never invokes the file command. This test makes sure the hardcoded map is working.