Check the command existance prior create and add Unit tests for the case

builder.go

@@ -72,7 +72,7 @@ func (builder *Builder) Create(config *Config) (*Container, error) {
 		builder.mergeConfig(config, img.Config)
 	}
 
-	if config.Cmd == nil {
+	if config.Cmd == nil || len(config.Cmd) == 0 {
 		return nil, fmt.Errorf("No command specified")
 	}
 

runtime.go

@@ -178,6 +178,10 @@ func (runtime *Runtime) LogToDisk(src *writeBroadcaster, dst string) error {
 }
 
 func (runtime *Runtime) Destroy(container *Container) error {
+	if container == nil {
+		return fmt.Errorf("The given container is <nil>")
+	}
+
 	element := runtime.getContainerElement(container.Id)
 	if element == nil {
 		return fmt.Errorf("Container %v not found - maybe it was already destroyed?", container.Id)

runtime_test.go

@@ -118,7 +118,10 @@ func TestRuntimeCreate(t *testing.T) {
 	if len(runtime.List()) != 0 {
 		t.Errorf("Expected 0 containers, %v found", len(runtime.List()))
 	}
-	container, err := NewBuilder(runtime).Create(&Config{
+
+	builder := NewBuilder(runtime)
+
+	container, err := builder.Create(&Config{
 		Image: GetTestImage(runtime).Id,
 		Cmd:   []string{"ls", "-al"},
 	},
@@ -157,6 +160,26 @@ func TestRuntimeCreate(t *testing.T) {
 	if !runtime.Exists(container.Id) {
 		t.Errorf("Exists() returned false for a newly created container")
 	}
+
+	// Make sure crete with bad parameters returns an error
+	_, err = builder.Create(
+		&Config{
+			Image: GetTestImage(runtime).Id,
+		},
+	)
+	if err == nil {
+		t.Fatal("Builder.Create should throw an error when Cmd is missing")
+	}
+
+	_, err = builder.Create(
+		&Config{
+			Image: GetTestImage(runtime).Id,
+			Cmd:   []string{},
+		},
+	)
+	if err == nil {
+		t.Fatal("Builder.Create should throw an error when Cmd is empty")
+	}
 }
 
 func TestDestroy(t *testing.T) {