t.Fatalf("write failed: %v", err)
	}
	args := []string{"run", "-covermode=" + testing.CoverMode(), src}
	cmd := exec.Command(testenv.GoToolPath(t), args...)
	cmd.Env = updateGoCoverDir(os.Environ(), dstdir, true)
	if b, err := cmd.CombinedOutput(); err != nil {
		t.Fatalf("go run failed (%v): %s", err, b)
	}

	// Pick out the generated meta-data file.
	files, err := os.ReadDir(dstdir)