Implement the 'shared' subcommand for mmutex

mmutex/cmd/mmutex/shared_test.go

Index: mmutex/cmd/mmutex/shared_test.go
diff --git a/mmutex/cmd/mmutex/exclusive_test.go b/mmutex/cmd/mmutex/shared_test.go
similarity index 51%
copy from mmutex/cmd/mmutex/exclusive_test.go
copy to mmutex/cmd/mmutex/shared_test.go
index f32e68004cd68d113e3175b646cef2f5b5b4f02f..2ef0f828ac5b71a75c4b7934a823d54225d672bc 100644
--- a/mmutex/cmd/mmutex/exclusive_test.go
+++ b/mmutex/cmd/mmutex/shared_test.go
@@ -28,8 +28,8 @@ import (
 	. "github.com/luci/luci-go/common/testing/assertions"
 )
 
-func TestMain(t *testing.T) {
-	Convey("RunExclusive executes the command", t, func(c C) {
+func TestShared(t *testing.T) {
+	Convey("RunShared executes the command", t, func() {
 		var tempDir string
 		var err error
 
@@ -41,22 +41,22 @@ func TestMain(t *testing.T) {
 		testFilePath := filepath.Join(tempDir, "test")
 		var command []string
 		if runtime.GOOS == "windows" {
-			command = []string{"cmd", "/c", "copy", "NUL", testFilePath}
+			command = createCommand([]string{"copy", "NUL", testFilePath})
 		} else {
-			command = []string{"touch", testFilePath}
+			command = createCommand([]string{"touch", testFilePath})
 		}
 
-		So(RunExclusive(command, 0, 0), ShouldBeNil)
+		So(RunShared(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("RunShared returns error from the command", t, func() {
+		So(RunShared([]string{"nonexistent_command"}, 0, 0), ShouldErrLike, "executable file not found")
 	})
 
-	Convey("RunExclusive times out if lock isn't released", t, func(c C) {
+	Convey("RunShared times out if an exclusive lock isn't released", t, func() {
 		var handle fslock.Handle
 		var err error
 
@@ -65,20 +65,32 @@ func TestMain(t *testing.T) {
 		}
 		defer handle.Unlock()
 
-		So(RunExclusive([]string{"echo", "should_fail"}, 0, 0), ShouldErrLike, "fslock: lock is held")
+		start := time.Now()
+		So(RunShared([]string{"echo", "should_fail"}, 5*time.Millisecond, 0), ShouldErrLike, "fslock: lock is held")
+		So(time.Now(), ShouldHappenOnOrAfter, start.Add(5*time.Millisecond))
 	})
 
-	Convey("RunExclusive respects timeout", t, func(c C) {
+	Convey("RunShared executes the command if shared lock already held", t, func() {
 		var handle fslock.Handle
 		var err error
 
-		if handle, err = fslock.Lock(LockFilePath); err != nil {
+		if handle, err = fslock.LockShared(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))
+		So(RunShared(createCommand([]string{"echo", "should_succeed"}), 0, 0), ShouldBeNil)
 	})
+
+	// TODO(charliea): Add a test to ensure that RunShared() treats the presence of a drain file the
+	// same as a held lock.
+
+	// TODO(charliea): Add a test to ensure that RunShared() uses the $CHOPS_SERVICE_LOCK environment
+	// variable to determine the directory for the lock and drain files.
+
+	// TODO(charliea): Add a test to ensure that RunShared() just acts as a passthrough if
+	// the $CHOPS_SERVICE_LOCK directory isn't set.
+
+	// TODO(charliea): Add a test to ensure that RunShared() just acts as a passthrough if
+	// the $CHOPS_SERVICE_LOCK directory doesn't exist.
 }