diff --git a/keygen/id_test.go b/keygen/id_test.go
new file mode 100644
index 0000000..f5d538f
--- /dev/null
+++ b/keygen/id_test.go
@@ -0,0 +1,34 @@
+package keygen
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestNext(t *testing.T) {
+	id := Next(24)
+	ipv4, err := getIPv4()
+
+	assert.Nil(t, err)
+	assert.GreaterOrEqual(t, time.Now().UnixNano()/1e6, int64(id>>int64(timeLeft))+twepoch)
+	assert.Equal(t, int(ipv4[3])%64, getWorkerNumber(id))
+	assert.Equal(t, 24, TableIdx(id))
+}
+
+func TestNextWithLargerCheck(t *testing.T) {
+	var lastId int64
+	tableIdx := int64(1)
+
+	for i := 0; i < 10000; i++ {
+		newId := Next(tableIdx)
+
+		if lastId >= newId {
+			t.Errorf("Expect new: %d > last: %d, but not.", newId, lastId)
+			break
+		}
+
+		lastId = newId
+	}
+}