filter(go): add go test filter

[mpecan]

Goal

Expand Go filters to cover go test -v — the verbose test output mode widely used in CI and agent contexts. Currently go/build.toml and go/vet.toml exist but test output has no filter.

Background

go test -v ./... on a large repo emits:

• === RUN TestFunctionName for every test
• --- PASS: TestFunctionName (0.00s) for every passing test
• All t.Log() / t.Logf() output captured during passing tests
• ok package/path 0.123s for every passing package

The Go team has an open proposal (golang/go#59201) for a -vf (verbose-when-fail) flag that would only show details for failing tests — a feature the community has wanted for years. gotestsum exists as a community workaround.

Filters to Add

go/test.toml — go test -v / go test -v ./...

• Skip: === RUN ... lines for passing tests, --- PASS: ... lines, t.Log output lines for passing tests, ok package summary lines when all pass
• Keep:
  • --- FAIL: ... lines
  • === RUN header for the failing test
  • All output lines between a failing === RUN and its --- FAIL (error details, stack traces)
  • FAIL\tpackage/path lines
  • panic: lines
  • The final FAIL or ok summary

Consider section parsing: track === RUN as section open, --- PASS as discard-section, --- FAIL as keep-section.

go/test-race.toml — go test -race

• Same as go/test.toml but also keep data race detector output (WARNING: DATA RACE blocks)

Fixture Files Needed

• tests/fixtures/go/test-all-pass.txt — verbose output with 50+ passing tests
• tests/fixtures/go/test-failure.txt — mixed passing and failing tests, failures with assertion details
• tests/fixtures/go/test-panic.txt — test that panics mid-execution

Acceptance Criteria

• --- PASS and === RUN lines for passing tests removed
• Failed test === RUN / --- FAIL lines and their captured output preserved
• panic: output always preserved
• Integration tests pass for all fixture files