diff --git a/util/id/id_internal_test.go b/util/id/id_internal_test.go
new file mode 100644
index 0000000..88091a9
--- /dev/null
+++ b/util/id/id_internal_test.go
@@ -0,0 +1,41 @@
+package id
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestHasNoCollisions(t *testing.T) {
+	tries := 100_000
+	used := make(map[string]bool, tries)
+	for i := 0; i < tries; i++ {
+		id := Must()
+		require.False(t, used[id], "shouldn't return colliding IDs")
+		used[id] = true
+	}
+}
+
+func TestFlatDistribution(t *testing.T) {
+	tries := 100_000
+	alphabet := "abcdefghij"
+	size := 10
+	chars := make(map[rune]int)
+	for i := 0; i < tries; i++ {
+		id := Must(Alphabet(alphabet), Size(size))
+		for _, r := range id {
+			chars[r]++
+		}
+	}
+
+	for _, count := range chars {
+		require.InEpsilon(t, size*tries/len(alphabet), count, .01, "should have flat distribution")
+	}
+}
+
+// Benchmark id generator
+func BenchmarkNanoid(b *testing.B) {
+	for n := 0; n < b.N; n++ {
+		_, _ = New()
+	}
+}
diff --git a/util/id/id_test.go b/util/id/id_test.go
new file mode 100644
index 0000000..e2f0c7f
--- /dev/null
+++ b/util/id/id_test.go
@@ -0,0 +1,68 @@
+package id_test
+
+import (
+	"strings"
+	"testing"
+	"unicode/utf8"
+
+	"github.com/stretchr/testify/assert"
+	id "github.com/unistack-org/micro/v3/util/id"
+)
+
+func TestGenerate(t *testing.T) {
+	t.Run("short alphabet", func(t *testing.T) {
+		alphabet := ""
+		_, err := id.New(id.Alphabet(alphabet), id.Size(32))
+		assert.Error(t, err, "should return error if the alphabet is too small")
+	})
+
+	t.Run("long alphabet", func(t *testing.T) {
+		alphabet := strings.Repeat("a", 256)
+		_, err := id.New(id.Alphabet(alphabet), id.Size(32))
+		assert.Error(t, err, "should return error if the alphabet is too long")
+	})
+
+	t.Run("negative ID length", func(t *testing.T) {
+		_, err := id.New(id.Alphabet("abcdef"), id.Size(-1))
+		assert.Error(t, err, "should return error if the requested ID length is invalid")
+	})
+
+	t.Run("happy path", func(t *testing.T) {
+		alphabet := "abcdef"
+		id, err := id.New(id.Alphabet(alphabet), id.Size(6))
+		assert.NoError(t, err, "shouldn't return error")
+		assert.Len(t, id, 6, "should return ID of requested length")
+		for _, r := range id {
+			assert.True(t, strings.ContainsRune(alphabet, r), "should use given alphabet")
+		}
+	})
+
+	t.Run("works with unicode", func(t *testing.T) {
+		alphabet := "🚀💩🦄🤖"
+		id, err := id.New(id.Alphabet(alphabet), id.Size(6))
+		assert.NoError(t, err, "shouldn't return error")
+		assert.Equal(t, utf8.RuneCountInString(id), 6, "should return ID of requested length")
+		for _, r := range id {
+			assert.True(t, strings.ContainsRune(alphabet, r), "should use given alphabet")
+		}
+	})
+}
+
+func TestNew(t *testing.T) {
+	t.Run("negative ID length", func(t *testing.T) {
+		_, err := id.New(id.Size(-1))
+		assert.Error(t, err, "should return error if the requested ID length is invalid")
+	})
+
+	t.Run("happy path", func(t *testing.T) {
+		nid, err := id.New()
+		assert.NoError(t, err, "shouldn't return error")
+		assert.Len(t, nid, id.DefaultSize, "should return ID of default length")
+	})
+
+	t.Run("custom length", func(t *testing.T) {
+		id, err := id.New(id.Size(6))
+		assert.NoError(t, err, "shouldn't return error")
+		assert.Len(t, id, 6, "should return ID of requested length")
+	})
+}