Flesh out the mmutex binary wrapper and test for existence of lockfile

mmutex/lib/flock_test.go

+// 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 (
+        "fmt"
+        . "github.com/smartystreets/goconvey/convey"
+        "io/ioutil"
+        "os"
+        "testing"

[iannucci, 2017/07/11 20:52:15]

imports should be separated basically like:

  <stdlib>

  <golang.org/x/... imports>

  <third-party>

  <luci-go>

  <app imports>

[charliea (OOO until 10-5), 2017/07/11 23:26:16]

Done.

+)
+
+func TestAcquireExclusiveLock(t *testing.T) {
+        lockDir, err := ioutil.TempDir("/tmp", "")
+        if err != nil {
+                t.Error("received error creating temporary testing directory")
+        }
+        defer os.Remove(lockDir)
+        path := lockDir + ".lock"
+
+        Convey("AcquireExclusiveLock errors if lock file doesn't exist", t, func(c C) {
+                So(AcquireExclusiveLock(path).Error(), ShouldEqual, fmt.Sprintf("cannot acquire lock on %s because file does not exist", path))

[iannucci, 2017/07/11 20:52:15]

add an import:

  . "github.com/luci/luci-go/common/testing/assertions"

Then:

  So(expression_resulting_in_error, ShouldErrLike, "some text in the error")

[charliea (OOO until 10-5), 2017/07/11 23:26:16]

Done.

+        })
+}