// It is not covered (yet) by the Go 1 compatibility guidelines.
func RegisterCover(c Cover) {
	cover = c
}

// mustBeNil checks the error and, if present, reports it and exits.
func mustBeNil(err error) {
	if err != nil {
		fmt.Fprintf(os.Stderr, "testing: %s\n", err)
		os.Exit(2)
	}
}