Make mmutex actually acquire and release file locks

mmutex/lib/flock_test.go

Index: mmutex/lib/flock_test.go
diff --git a/mmutex/lib/flock_test.go b/mmutex/lib/flock_test.go
deleted file mode 100644
index d3b848e4ff90cbf8e49015eb39ca959ae2415f9a..0000000000000000000000000000000000000000
--- a/mmutex/lib/flock_test.go
+++ /dev/null
@@ -1,28 +0,0 @@
-// Copyright 2017 The LUCI Authors. All rights reserved.
-// Use of this source code is governed under the Apache License, Version 2.0
-// that can be found in the LICENSE file.
-
-package lib
-
-import (
-	"io/ioutil"
-	"os"
-	"testing"
-
-	. "github.com/smartystreets/goconvey/convey"
-
-	. "github.com/luci/luci-go/common/testing/assertions"
-)
-
-func TestAcquireExclusiveLock(t *testing.T) {
-	lockDir, err := ioutil.TempDir("", "")
-	if err != nil {
-		t.Error("received error creating temporary testing directory")
-	}
-	defer os.Remove(lockDir)
-	path := lockDir + "test.lock"
-
-	Convey("AcquireExclusiveLock errors if lock file doesn't exist", t, func(c C) {
-		So(AcquireExclusiveLock(path), ShouldErrLike, "lock file does not exist")
-	})
-}