Add test case for issue 219

Signed-off-by: Golang Lemonade <[email protected]>

clientv2/client_test.go

@@ -568,6 +568,7 @@ func TestMarshalJSONValueType(t *testing.T) {
 			if !cmp.Equal(tt.want, got) {
 				t.Errorf("MarshalJSON() = %v, want %v", got, tt.want)
 			}
+
 		})
 	}
 }
@@ -578,6 +579,13 @@ func TestMarshalJSON(t *testing.T) {
 		Name   string `json:"name"`
 		Number Number `json:"number"`
 	}
+
+	// example nested struct
+	type WhereInput struct {
+		Not *WhereInput `json:"not,omitempty"`
+		ID  *string     `json:"id,omitempty"`
+	}
+
 	testDate := time.Date(2021, 1, 1, 0, 0, 0, 0, time.UTC)
 	type args struct {
 		v any
@@ -608,6 +616,23 @@ func TestMarshalJSON(t *testing.T) {
 			},
 			want: []byte(`{"operationName":"query", "query":"query ($input: Number!) { input }","variables":{"input":"TWO"}}`),
 		},
+		{
+			name: "marshal nested",
+			args: args{
+				v: Request{
+					OperationName: "query",
+					Query:         `query ($input: Number!) { input }`,
+					Variables: map[string]any{
+						"where": WhereInput{
+							Not: &WhereInput{
+								ID: &[]string{"1"}[0],
+							},
+						},
+					},
+				},
+			},
+			want: []byte(`{"operationName":"query", "query":"query ($input: Number!) { input }","variables":{"where":{"not":{"id":"1"}}}}`),
+		},
 		{
 			name: "marshal a struct with custom marshaler",
 			args: args{