diff --git a/twitter/ruby_date.go b/twitter/ruby_date.go
index efbd03c..299942a 100644
--- a/twitter/ruby_date.go
+++ b/twitter/ruby_date.go
@@ -21,9 +21,21 @@ import (
 
 type RubyDate time.Time
 
+func (t *RubyDate) Iso8601() string {
+	return time.Time(*t).Format("2006-01-02T15:04:05-07:00")
+}
+
+func (t *RubyDate) String() string {
+	return time.Time(*t).Format(time.RubyDate)
+}
+
+func (t *RubyDate) Equal(u RubyDate) bool {
+	return time.Time(*t).Equal(time.Time(u))
+}
+
 func (t *RubyDate) UnmarshalJSON(buf []byte) error {
 	s := bytes.Trim(buf, `"`)
-	parsed, err := time.Parse(time.RubyDate, string(s))
+	parsed, err := time.ParseInLocation(time.RubyDate, string(s), time.UTC)
 	if err != nil {
 		return err
 	}
diff --git a/twitter/ruby_date_test.go b/twitter/ruby_date_test.go
new file mode 100644
index 0000000..f4bb7ec
--- /dev/null
+++ b/twitter/ruby_date_test.go
@@ -0,0 +1,94 @@
+// Copyright 2022 Akiomi Kamakura
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package twitter
+
+import (
+	"encoding/json"
+	"testing"
+	"time"
+)
+
+type TestSchema struct {
+	CreatedAt RubyDate `json:"created_at"`
+}
+
+func TestString(t *testing.T) {
+	d := RubyDate(time.Date(2013, 8, 19, 2, 4, 28, 0, time.UTC))
+	expected := "Mon Aug 19 02:04:28 +0000 2013"
+	actual := d.String()
+	if actual != expected {
+		t.Errorf("Expect RubyDate#String() = \"%s\", but got \"%s\"", expected, actual)
+		return
+	}
+}
+
+func TestIso8601(t *testing.T) {
+	d := RubyDate(time.Date(2013, 8, 19, 2, 4, 28, 0, time.UTC))
+	expected := "2013-08-19T02:04:28+00:00"
+	actual := d.Iso8601()
+	if actual != expected {
+		t.Errorf("Expect RubyDate#Iso8601() = \"%s\", but got \"%s\"", expected, actual)
+		return
+	}
+}
+
+func TestEqual(t *testing.T) {
+	examples := map[string]struct {
+		this     RubyDate
+		that     RubyDate
+		expected bool
+	}{
+		"true": {
+			this:     RubyDate(time.Date(2013, 8, 19, 2, 4, 28, 0, time.UTC)),
+			that:     RubyDate(time.Date(2013, 8, 19, 2, 4, 28, 0, time.UTC)),
+			expected: true,
+		},
+		"false": {
+			this:     RubyDate(time.Date(2013, 8, 19, 2, 4, 28, 0, time.UTC)),
+			that:     RubyDate(time.Date(2013, 8, 19, 2, 4, 28, 1, time.UTC)),
+			expected: false,
+		},
+	}
+
+	for name, e := range examples {
+		t.Run(name, func(t *testing.T) {
+			actual := e.this.Equal(e.that)
+			if actual != e.expected {
+				t.Errorf("Expect RubyDate#Equal() = %v, but got %v", e.expected, actual)
+				return
+			}
+		})
+	}
+}
+
+func TestUnmarshall(t *testing.T) {
+	jsonString := `{
+    "created_at": "Mon Aug 19 02:04:28 +0000 2013"
+  }`
+
+	schema := new(TestSchema)
+	err := json.Unmarshal([]byte(jsonString), &schema)
+	if err != nil {
+		t.Errorf("Expect Query#Encode() not to return error object, but got \"%v\"", err)
+		return
+	}
+
+	expected := RubyDate(time.Date(2013, 8, 19, 2, 4, 28, 0, time.UTC))
+	actual := schema.CreatedAt
+	if !actual.Equal(expected) {
+		t.Errorf("Expect RubyDate#Unmarshal() = \"%v\", but got \"%v\"", expected, actual)
+		return
+	}
+}