Focus on a specific test file

[axelson]

Would a PR to always focus on a specific file be accepted? My use case is that often when editing a module like a.ex I want to run a test from foo_test.exs instead of a_test.exs, also my test suite is too long to want to run all tests after every change. I have a first-pass at an implementation but representing the focus by a naive struct didn't come out very elegant so I think I want to tweak it before submitting a PR.

[glittershark]

Absolutely, would love a PR for that

[axelson]

Great! I'll work on cleaning it up to a workable state.

By the way thanks for being active in this project, I think it's a super neat dev tool!