internal/coverage/cfile: snapshot test is brittle w/ respect to -coverpkg

[thanm]

At tip, if you run the internal/coverage/cfile tests with -coverpkg set to something that does include cfile, you get:

     $ cd `go env GOROOT`
     $ cd src/internal/coverage
     $ go test -coverpkg=internal/coverage/decodecounter ./...
     ...
      --- FAIL: TestCoverageSnapshot (0.00s)
          ts_test.go:102: 0.276074 0.276074
          ts_test.go:104: erroneous snapshots, C1 >= C2 = true C1=0.276074 C2=0.276074

This is happening because the test is calling out to a function that it expects will bump up the coverage percentage, but that func is not being instrumented.

The test needs to be rewritten to make it a bit more robust.

[gabyhelp]

Similar Issues

• Coverage incorrectly reported as 100% ( go test cover) #26760
• cmd/go: go test -cover loses coverage of some inlined functions #23314
• cmd/go: go 1.22.0: go test throws errors when processing folders not listed in coverpkg argument #65653
• cmd/covdata: percent does not support -coverpkg #66464
• cmd/go: go test using -coverpkg can change the test result #36541

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[gopherbot]

Change https://go.dev/cl/592200 mentions this issue: internal/coverage/cfile: harden the coverage snapshot test