func mustBeNil(err error) {
	if err != nil {
		fmt.Fprintf(os.Stderr, "testing: %s\n", err)
		os.Exit(2)
	}
}

// coverReport reports the coverage percentage and writes a coverage profile if requested.
func coverReport() {
	if goexperiment.CoverageRedesign {
		coverReport2()
		return
	}
	var f *os.File
	var err error
	if *coverProfile != "" {
		f, err = os.Create(toOutputDir(*coverProfile))

		if err = m.deps.WriteProfileTo("mutex", f, 0); err != nil {
			fmt.Fprintf(os.Stderr, "testing: can't write %s: %s\n", *mutexProfile, err)
			os.Exit(2)
		}
		f.Close()
	}
	if CoverMode() != "" {
		coverReport()
	}
}

// toOutputDir returns the file name relocated, if required, to outputDir.
// Simple implementation to avoid pulling in path/filepath.
func toOutputDir(path string) string {

	if mode == "" {
		return
	}
	cover2.mode = mode
	cover2.tearDown = tearDown
	cover2.snapshotcov = snapcov
}

// coverReport2 invokes a callback in _testmain.go that will
// emit coverage data at the point where test execution is complete,
// for "go test -cover" runs.
func coverReport2() {
	if !goexperiment.CoverageRedesign {
		panic("unexpected")
	}