always update docker image when :latest tag

shared/build/build.go

@@ -234,8 +234,8 @@ func (b *Builder) setup() error {
 	log.Info("creating build image")
 
 	// check for build container (ie bradrydzewski/go:1.2)
-	// and download if it doesn't already exist
+	// and download if it doesn't already exist or it's :latest tag
-	if _, err := b.dockerClient.Images.Inspect(b.Build.Image); err == docker.ErrNotFound {
+	if _, err := b.dockerClient.Images.Inspect(b.Build.Image); err == docker.ErrNotFound || strings.HasSuffix(b.Build.Image, ":latest") {
 		// download the image if it doesn't exist
 		if err := b.dockerClient.Images.Pull(b.Build.Image); err != nil {
 			return fmt.Errorf("Error: Unable to pull image %s. %s", b.Build.Image, err)

shared/build/build_test.go

@@ -224,6 +224,29 @@ func TestSetupErrorImagePull(t *testing.T) {
 	}
 }
 
+// TestSetupErrorUpdate will test our ability to handle a
+// failure when the build image cannot be updated
+func TestSetupErrorUpdate(t *testing.T) {
+	setup()
+	defer teardown()
+
+	mux.HandleFunc("/v1.9/images/create", func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusBadRequest)
+	})
+
+	b := Builder{}
+	b.Repo = &repo.Repo{}
+	b.Repo.Path = "git://github.com/drone/drone.git"
+	b.Build = &script.Build{}
+	b.Build.Image = "bradrydzewski/go:latest"
+	b.dockerClient = client
+
+	var got, want = b.setup(), fmt.Errorf("Error: Unable to pull image bradrydzewski/go:latest. %s", docker.ErrBadRequest)
+	if got == nil || got.Error() != want.Error() {
+		t.Errorf("Expected error %s, got %s", want, got)
+	}
+}
+
 // TestSetupErrorBuild will test our ability to handle a failure
 // when creating a Docker image with the injected build script,
 // ssh keys, etc.