diff --git a/core/mapping/unmarshaler_test.go b/core/mapping/unmarshaler_test.go
index b756fba6..0c50d269 100644
--- a/core/mapping/unmarshaler_test.go
+++ b/core/mapping/unmarshaler_test.go
@@ -12,6 +12,7 @@ import (
 
 	"github.com/google/uuid"
 	"github.com/stretchr/testify/assert"
+
 	"github.com/zeromicro/go-zero/core/stringx"
 )
 
@@ -4384,3 +4385,44 @@ func BenchmarkUnmarshal(b *testing.B) {
 		UnmarshalKey(data, &an)
 	}
 }
+
+func TestFillDefaultUnmarshal(t *testing.T) {
+	fillDefaultUnmarshal := NewUnmarshaler(jsonTagKey, WithDefault())
+	t.Run("nil", func(t *testing.T) {
+		type St struct{}
+		err := fillDefaultUnmarshal.Unmarshal(map[string]any{}, St{})
+		assert.Error(t, err)
+	})
+
+	t.Run("not nil", func(t *testing.T) {
+		type St struct{}
+		err := fillDefaultUnmarshal.Unmarshal(map[string]any{}, &St{})
+		assert.NoError(t, err)
+	})
+
+	t.Run("default", func(t *testing.T) {
+		type St struct {
+			A string `json:",default=a"`
+			B string
+		}
+		var st St
+		err := fillDefaultUnmarshal.Unmarshal(map[string]any{}, &st)
+		assert.NoError(t, err)
+		assert.Equal(t, st.A, "a")
+	})
+
+	t.Run("env", func(t *testing.T) {
+		type St struct {
+			A string `json:",default=a"`
+			B string
+			C string `json:",env=TEST_C"`
+		}
+		t.Setenv("TEST_C", "c")
+
+		var st St
+		err := fillDefaultUnmarshal.Unmarshal(map[string]any{}, &st)
+		assert.NoError(t, err)
+		assert.Equal(t, st.A, "a")
+		assert.Equal(t, st.C, "c")
+	})
+}