diff --git a/rule/max_bound_test.go b/rule/max_bound_test.go
index dd6786c..c050f84 100644
--- a/rule/max_bound_test.go
+++ b/rule/max_bound_test.go
@@ -70,3 +70,12 @@ func TestMaxBoundWithInvalidParam(t *testing.T) {
 		}
 	}
 }
+
+func TestMaxBoundError(t *testing.T) {
+	err := &ErrMaxBound{Field: "text", Value: "2", Bound: 1}
+	got := err.Error()
+	want := "the value 2 in field text has character limit greater than 1"
+	if got != want {
+		t.Errorf(`&ErrMaxBound{Field: "text", Value: "2", Bound: 1}.Error(), got: %v, want: %v`, got, want)
+	}
+}
diff --git a/rule/min_bound_test.go b/rule/min_bound_test.go
index 3ec6325..9781f01 100644
--- a/rule/min_bound_test.go
+++ b/rule/min_bound_test.go
@@ -68,3 +68,12 @@ func TestMinBoundWithInvalidParam(t *testing.T) {
 		}
 	}
 }
+
+func TestMinBoundError(t *testing.T) {
+	err := &ErrMinBound{Field: "text", Value: "2", Bound: 1}
+	got := err.Error()
+	want := "the value 2 in field text has character limit less than 1"
+	if got != want {
+		t.Errorf(`&ErrMinBound{Field: "text", Value: "2", Bound: 1}.Error(), got: %v, want: %v`, got, want)
+	}
+}