diff --git a/generator_test.go b/generator_test.go
new file mode 100644
index 0000000..aa453ec
--- /dev/null
+++ b/generator_test.go
@@ -0,0 +1,25 @@
+package ID
+
+import "testing"
+
+func TestUnique(t *testing.T) {
+	gen := New(0)
+	ids := make(map[Type]struct{})
+
+	start := gen.Next()
+	ids[start] = struct{}{}
+
+	for current := gen.Next(); current != start; current = gen.Next() {
+		if _, ok := ids[current]; ok {
+			t.Fatal("generator returned known id")
+		}
+
+		ids[current] = struct{}{}
+	}
+
+	if len(ids) == 1 {
+		t.Error("generator always returns same id")
+	}
+
+	t.Log("generator returned", len(ids), "ids")
+}