Make mmutex actually acquire and release file locks

mmutex/cmd/mmutex/exclusive_test.go

Index: mmutex/cmd/mmutex/exclusive_test.go
diff --git a/mmutex/cmd/mmutex/exclusive_test.go b/mmutex/cmd/mmutex/exclusive_test.go
new file mode 100644
index 0000000000000000000000000000000000000000..f32e68004cd68d113e3175b646cef2f5b5b4f02f
--- /dev/null
+++ b/mmutex/cmd/mmutex/exclusive_test.go
@@ -0,0 +1,84 @@
+// Copyright 2017 The LUCI Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"runtime"
+	"testing"
+	"time"
+
+	"github.com/danjacques/gofslock/fslock"
+	. "github.com/smartystreets/goconvey/convey"
+
+	. "github.com/luci/luci-go/common/testing/assertions"
+)
+
+func TestMain(t *testing.T) {
+	Convey("RunExclusive executes the command", t, func(c C) {
+		var tempDir string
+		var err error
+
+		if tempDir, err = ioutil.TempDir("", ""); err != nil {
+			panic(err)
+		}
+		defer os.Remove(tempDir)
+
+		testFilePath := filepath.Join(tempDir, "test")
+		var command []string
+		if runtime.GOOS == "windows" {
+			command = []string{"cmd", "/c", "copy", "NUL", testFilePath}
+		} else {
+			command = []string{"touch", testFilePath}
+		}
+
+		So(RunExclusive(command, 0, 0), ShouldBeNil)
+
+		_, err = os.Stat(testFilePath)
+		So(err, ShouldBeNil)
+	})
+
+	Convey("RunExclusive returns error from the command", t, func(c C) {
+		So(RunExclusive([]string{"nonexistent_command"}, 0, 0), ShouldErrLike, "executable file not found")
+	})
+
+	Convey("RunExclusive times out if lock isn't released", t, func(c C) {
+		var handle fslock.Handle
+		var err error
+
+		if handle, err = fslock.Lock(LockFilePath); err != nil {
+			panic(err)
+		}
+		defer handle.Unlock()
+
+		So(RunExclusive([]string{"echo", "should_fail"}, 0, 0), ShouldErrLike, "fslock: lock is held")
+	})
+
+	Convey("RunExclusive respects timeout", t, func(c C) {
+		var handle fslock.Handle
+		var err error
+
+		if handle, err = fslock.Lock(LockFilePath); err != nil {
+			panic(err)
+		}
+		defer handle.Unlock()
+
+		start := time.Now()
+		RunExclusive([]string{"echo", "should_fail"}, 5*time.Millisecond, 0)
+		So(time.Now(), ShouldHappenOnOrAfter, start.Add(5*time.Millisecond))
+	})
+}