[TE-6238] Prepend ./ when collecting selectors for RSpec

[nprizal]

Description

RSpec's selector based splitting was sending selectors without RSpec's native ./ prefix, so they didn't match test.selector.primary on the Test Engine side. This meant test plans came back with no historical duration, since nothing matched.

GetSelectors() now prepends ./ to each discovered file, matching the format RSpec itself reports.

Context

Found this while testing selector based splitting for rspec in buildkite/buildkite (build) — the test plan came back without historical duration. test.selector.primary is currently set manually from the file name RSpec reports (see test_engine_helper.rb), which includes RSpec's ./ prefix, but bktec wasn't including it when requesting the plan.

The sentiment is that we want test.selector.primary to stay "pure", so we're not applying location prefix to selectors for splitting purposes, even though we still want to support location prefix for result reporting. This is discussed further in this doc.

Testing

Updated TestRspecGetSelectors to assert the ./ prefix is included.

[buildsworth-bk-app]

Bug fix with a focused test covering the changed RSpec selector format, and no API surface change beyond the selector values sent for RSpec splitting.

Want to dig deeper? The full session log is attached to this Buildkite build. Download the session file and open a new pi session with it:

Download the buildsworth logs from build 2203, then answer my questions about the findings.