This issue is hurting my brain a little, but I'll try and explain it. It's a regression introduced by https://github.com/rails/rails/pull/44290, in the following conditions:

- You use `minitest/spec` (either direction or via a wrapper like [`minitest-spec-rails`](https://github.com/metaskills/minitest-spec-rails))
- You run tests using a regex filter to identify which tests to run (either directly or via a wrapper like [`m`](https://github.com/qrush/m))

Since https://github.com/rails/rails/pull/44290 you could not execute a test that has a space in its name using the regex filter method. This is because:

- https://github.com/rails/rails/blob/444df0eee1b537ecaa11509e819b071d4e87b519/activesupport/lib/active_support/testing/declarative.rb#L6 doesn't define the `test` method if `Spec` is defined. Recall that the `test` method does 2 things: it defines the test, but it also replaces spaces with underscores in the test method name.
- In minitest specs, you use `it` to define tests. `it` [generates a test method name](https://github.com/minitest/minitest/blob/a9fa045044b4210cfd21a512b06d1a4527d709ba/lib/minitest/spec.rb#L223..L229) by taking user input and prepending `test_` and a number. It does *not* replace spaces with underscores. So the test method is defined as `"test_002_foo bar"`.
- Since https://github.com/rails/rails/pull/44290

 when you provide the test runner a filter it replaces spaces with underscores before passing the filter onto minitest. For example, the filter might become `"/test_002_foo_bar/"`.
- Minitest thus can't find the test method and doesn't run it.

The issue is in `escape_declarative_test_filter`. Rather than converting spaces to underscores, it should match both spaces *and* underscores. This covers all use cases.

Co-authored-by: jonathanhefner <jonathan@hefner.pro>