enhance: maputil: add NewMapStringSlice()

type/maputil/map_string_slice.go

@@ -8,6 +8,10 @@ import (
 
 type MapStringSlice map[string][]string
 
+func NewMapStringSlice() MapStringSlice {
+	return MapStringSlice{}
+}
+
 func (mss MapStringSlice) Add(key, value string) {
 	if _, ok := mss[key]; !ok {
 		mss[key] = []string{value}

type/maputil/map_string_slice_test.go

@@ -0,0 +1,36 @@
+package maputil
+
+import (
+	"strings"
+	"testing"
+)
+
+var mssTests = []struct {
+	data           map[string][]string
+	sortTestKey    string
+	sortTestValues []string
+}{
+	{
+		data: map[string][]string{
+			"foo": {"foo", "bar", "baz"}},
+		sortTestKey:    "foo",
+		sortTestValues: []string{"bar", "baz", "foo"}},
+}
+
+func TestMapStringSlice(t *testing.T) {
+	for _, tt := range mssTests {
+		mss := NewMapStringSlice()
+		for key, vals := range tt.data {
+			for _, val := range vals {
+				mss.Add(key, val)
+			}
+		}
+		mss.Sort(true)
+		valsWant := strings.Join(tt.sortTestValues, ",")
+		valsTry := strings.Join(mss[tt.sortTestKey], ",")
+		if valsTry != valsWant {
+			t.Errorf("maputil.MapStringSlice.Sort() Fail: want [%s], got [%s]",
+				valsWant, valsTry)
+		}
+	}
+}