diff --git a/helper_test.go b/helper_test.go
new file mode 100644
index 0000000..0f81a20
--- /dev/null
+++ b/helper_test.go
@@ -0,0 +1,16 @@
+package main
+
+import (
+	"testing"
+)
+
+// test this file: go test helper_test.go helper.go -v
+// test one function: go test -run TestGetFileContentType helper_test.go helper.go -v
+func TestGetFileContentType(t *testing.T) {
+	var zero = []byte("hello")
+	r := GetFileContentType(zero)
+	if r != "text/plain; charset=utf-8" {
+		t.Errorf("Test error for %s", t.Name())
+	}
+
+}
diff --git a/update.go b/update.go
index e897d65..033b292 100644
--- a/update.go
+++ b/update.go
@@ -15,7 +15,7 @@ import (
 func autoUpdate() {
 	defer func() {
 		if err := recover(); err != nil {
-			log.Errorf("Download error.", err)
+			log.Errorf("Download error: %s", err)
 		}
 	}()
 
@@ -45,7 +45,7 @@ func autoUpdate() {
 	log.Info("Downloading binary to update...")
 	resp, _ := http.Get(releaseUrl)
 	if resp.StatusCode != 200 {
-		log.Debug("%s-%s not found on release.", runtime.GOOS, runtime.GOARCH)
+		log.Debugf("%s-%s not found on release.", runtime.GOOS, runtime.GOARCH)
 		return
 	}
 	data, _ := ioutil.ReadAll(resp.Body)