Add tests for Int32.compareTo.
diff --git a/test/int32_test.dart b/test/int32_test.dart
index 4571bbd..f2be733 100644
--- a/test/int32_test.dart
+++ b/test/int32_test.dart
@@ -154,6 +154,18 @@
   });
 
   group("comparison operators", () {
+    test("compareTo", () {
+      expect(new Int32(0).compareTo(-1), 1);
+      expect(new Int32(0).compareTo(0), 0);
+      expect(new Int32(0).compareTo(1), -1);
+      expect(new Int32(0).compareTo(new Int32(-1)), 1);
+      expect(new Int32(0).compareTo(new Int32(0)), 0);
+      expect(new Int32(0).compareTo(new Int32(1)), -1);
+      expect(new Int32(0).compareTo(new Int64(-1)), 1);
+      expect(new Int32(0).compareTo(new Int64(0)), 0);
+      expect(new Int32(0).compareTo(new Int64(1)), -1);
+    });
+
     test("<", () {
       expect(new Int32(17) < new Int32(18), true);
       expect(new Int32(17) < new Int32(17), false);