print MDTEST_TEST_FILTER value in single-quotes (and escaped)

[ericmarkmartin]

Summary

If an mdtest fails, the error output will include an example command that can be run to re-run just the failing test, e.g

To rerun this specific test, set the environment variable: MDTEST_TEST_FILTER="sync.md - With statements - Context manager with non-callable `__exit__` attribute"
MDTEST_TEST_FILTER="sync.md - With statements - Context manager with non-callable `__exit__` attribute" cargo test -p red_knot_python_semantic --test mdtest -- mdtest__with_sync

This is very helpful, but because we're printing the envvar value surrounded in double-quotes, the bits between backticks in this example get interpreted as a shell interpolation. When running this in zsh, for example, I see

❯ MDTEST_TEST_FILTER="sync.md - With statements - Context manager with non-callable `__exit__` attribute" cargo test -p red_knot_python_semantic --test mdtest -- mdtest__with_sync  
zsh: command not found: __exit__
   Compiling red_knot_python_semantic v0.0.0 (/home/ericmarkmartin/Development/ruff/crates/red_knot_python_semantic)
   Compiling red_knot_test v0.0.0 (/home/ericmarkmartin/Development/ruff/crates/red_knot_test)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 6.09s
     Running tests/mdtest.rs (target/debug/deps/mdtest-149b8f9d937e36bc)

running 1 test
test mdtest__with_sync ... ok

¹

This is a minor annoyance which we can solve by using single-quotes instead of double-quotes for this string. To do so safely, we also escape single-quotes possibly contained within the string.

There is a shell-quote crate, which seems to handle all this escaping stuff for you but fixing this issue perfectly isn't a big deal (if there are more things to escape we can deal with it then), so adding a new dependency (even a dev one) seemed overkill.

Test Plan

I broke the ## Context manager with non-callable `__exit__` attribute test by deleting the error assertion, then successfully ran the new command it printed out.

Footnotes

1. The filter does still work---it turns out that the filter MDTEST_TEST_FILTER="sync.md - With statements - Context manager with non-callable attribute" (what you get after the failed interpolation) is still good enough ↩

[MichaReiser]

Thanks. I verified that this doesn't break fish shell.