common using function lock goroutine 132 [semacquire] issue ono go parallel testing

Code

func RunXXXXCli(args []string, stdinInput string) ([]byte, string, error) {
    mmutex.Lock()
    cmd := exec.Command("path_to_xxxx_cli", args...)
    cmd.Stdin = strings.NewReader(stdinInput)
    res, err := cmd.CombinedOutput()
    mmutex.Unlock()
    return res, err
}

This cli shouldn't run in parallel and the test itself should run in parallel for faster result creation. For that I have locked the code at the beginning of the function and unlocked after the end of the function.

This does not happen always but happens rarely on a fast computer. (RAM: 64GB, Processor: 2.5GHz Intel Xeon).

Error Log

goroutine 132 [semacquire]:
sync.runtime_SemacquireMutex(0x572959c, 0x0, 0x1)
    /usr/local/Cellar/go/1.13/libexec/src/runtime/sema.go:71 +0x47
sync.(*Mutex).lockSlow(0x5729598)
    /usr/local/Cellar/go/1.13/libexec/src/sync/mutex.go:138 +0xfc
sync.(*Mutex).Lock(...)
    /usr/local/Cellar/go/1.13/libexec/src/sync/mutex.go:81

This is very annoying issue, and I have been struggling for more than 2 weeks. This started to typically happen when the number of parallel running test cases increased. Is there anyone who has met similar issues before?