diff --git a/cache_test.go b/cache_test.go
new file mode 100644
index 0000000..1dd2252
--- /dev/null
+++ b/cache_test.go
@@ -0,0 +1,31 @@
+package time_arrow
+
+import (
+	"testing"
+	"time"
+)
+
+func Test_cache_IsExpired(t *testing.T) {
+	cachet := cache{}
+	if cachet.IsExpired() {
+		cachet.SetData("hello", time.Second*5)
+	}
+
+	time.Sleep(time.Second * 1)
+	data := cachet.GetData()
+	if cachet.IsExpired() {
+		t.Error("cache should not be expired 1")
+	}
+	if data != "hello" {
+		t.Error("cache should not be expired 2")
+	}
+
+	time.Sleep(time.Second * 5)
+	data = cachet.GetData()
+	if !cachet.IsExpired() {
+		t.Error("cache should be expired 1 ")
+	}
+	if data != "" {
+		t.Error("cache should be expired 2")
+	}
+}
diff --git a/core.go b/core.go
index 2374be7..22687aa 100644
--- a/core.go
+++ b/core.go
@@ -392,6 +392,9 @@ func GetHolidaysDataWithCache() ([]HolidaysItem, error) {
 	data := holidayCache.GetData()
 	var result []HolidaysItem
 	err := json.Unmarshal([]byte(data), &result)
+	if len(data) == 0 {
+		panic("GetHolidaysDataWithCache json unmarshal error")
+	}
 	return result, err
 }