fix: potential error in combine (#525)

add ut for combine and split

engine/virt/helper.go

@@ -61,5 +61,11 @@ func splitUserImage(combined string) (user, imageName string, err error) {
 }
 
 func combineUserImage(user, imageName string) string {
+	if len(imageName) < 1 {
+		return ""
+	}
+	if len(user) < 1 {
+		return imageName
+	}
 	return fmt.Sprintf("%s%s%s", user, sep, imageName)
 }

engine/virt/helper_test.go

@@ -0,0 +1,40 @@
+package virt
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestCombineUserImage(t *testing.T) {
+	user := "user"
+	image := "image"
+
+	combine := combineUserImage(user, image)
+	require.Equal(t, "user@image", combine)
+	u, i, err := splitUserImage(combine)
+	require.NoError(t, err)
+	require.Equal(t, user, u)
+	require.Equal(t, image, i)
+
+	combine = combineUserImage("", image)
+	require.Equal(t, image, combine)
+	u, i, err = splitUserImage(combine)
+	require.NoError(t, err)
+	require.Equal(t, "", u)
+	require.Equal(t, image, i)
+
+	combine = combineUserImage(user, "")
+	require.Equal(t, "", combine)
+	u, i, err = splitUserImage(combine)
+	require.Error(t, err)
+
+	combine = combineUserImage("", "")
+	require.Equal(t, "", combine)
+
+	u, i, err = splitUserImage("@")
+	require.Error(t, err)
+
+	u, i, err = splitUserImage("hello@")
+	require.Error(t, err)
+}