add stringmap test

sliceutil/sliceutil_test.go

@@ -438,6 +438,7 @@ func TestFilterInt(t *testing.T) {
 		})
 	}
 }
+
 func TestChooseString(t *testing.T) {
 	tests := []struct {
 		in   []string
@@ -500,3 +501,30 @@ func TestRemoveString(t *testing.T) {
 		})
 	}
 }
+
+func TestStringMap(t *testing.T) {
+	cases := []struct {
+		in   []string
+		want []string
+		f    func(string) string
+	}{
+		{
+			in:   []string{"a", "b", "c"},
+			want: []string{"", "", ""},
+			f:    func(string) string { return "" },
+		},
+		{
+			in:   []string{"a", "b", "c"},
+			want: []string{"aa", "bb", "cc"},
+			f:    func(c string) string { return c + c },
+		},
+	}
+	for _, tc := range cases {
+		t.Run("", func(t *testing.T) {
+			out := StringMap(tc.in, tc.f)
+			if !reflect.DeepEqual(tc.want, out) {
+				t.Errorf("\nout:  %#v\nwant: %#v\n", out, tc.want)
+			}
+		})
+	}
+}