diff --git a/objectid.py b/objectid.py
index af981441d..269eda06b 100644
--- a/objectid.py
+++ b/objectid.py
@@ -2,11 +2,7 @@
 
 import random
 import types
-import unittest
-
-class InvalidId(ValueError):
-    """Raised when trying to create an ObjectId from invalid data.
-    """
+from errors import InvalidId
 
 class ObjectId(object):
     """A Mongo ObjectId.
@@ -32,13 +28,13 @@ class ObjectId(object):
         """
         # TODO for now, just generate 12 random bytes. this will change when we decide on an _id algorithm...
         self.__new = True
-        id = ""
+        oid = ""
         for _ in range(12):
-            id += chr(random.randint(0, 255))
+            oid += chr(random.randint(0, 255))
 
-        self.__id = id
+        self.__id = oid
 
-    def __validate(self, id):
+    def __validate(self, oid):
         """Validate and use the given id for this ObjectId.
 
         Raises TypeError if id is not an instance of (str, ObjectId) and
@@ -48,15 +44,15 @@ class ObjectId(object):
         - `id`: a valid ObjectId
         """
         self.__new = False
-        if isinstance(id, ObjectId):
-            self.__id = id.__id
-        elif isinstance(id, types.StringType):
-            if len(id) == 12:
-                self.__id = id
+        if isinstance(oid, ObjectId):
+            self.__id = oid.__id
+        elif isinstance(oid, types.StringType):
+            if len(oid) == 12:
+                self.__id = oid
             else:
-                raise InvalidId("%s is not a valid ObjectId" % id)
+                raise InvalidId("%s is not a valid ObjectId" % oid)
         else:
-            raise TypeError("id must be an instance of (str, ObjectId), not %s" % type(id))
+            raise TypeError("id must be an instance of (str, ObjectId), not %s" % type(oid))
 
     def __str__(self):
         return self.__id
@@ -76,45 +72,3 @@ class ObjectId(object):
         """Return True if this ObjectId has not been used as an _id field.
         """
         return self.__new
-
-class TestObjectId(unittest.TestCase):
-    def setUp(self):
-        pass
-
-    def test_creation(self):
-        self.assertRaises(TypeError, ObjectId, 4)
-        self.assertRaises(TypeError, ObjectId, u"hello")
-        self.assertRaises(TypeError, ObjectId, 175.0)
-        self.assertRaises(TypeError, ObjectId, {"test": 4})
-        self.assertRaises(TypeError, ObjectId, ["something"])
-        self.assertRaises(InvalidId, ObjectId, "")
-        self.assertRaises(InvalidId, ObjectId, "12345678901")
-        self.assertRaises(InvalidId, ObjectId, "1234567890123")
-        self.assertTrue(ObjectId())
-        self.assertTrue(ObjectId("123456789012"))
-        a = ObjectId()
-        self.assertTrue(ObjectId(a))
-
-    def test_repr_str(self):
-        self.assertEqual(repr(ObjectId("123456789012")), "ObjectId('123456789012')")
-        self.assertEqual(str(ObjectId("123456789012")), "123456789012")
-
-    def test_cmp(self):
-        a = ObjectId()
-        self.assertEqual(a, ObjectId(a))
-        self.assertEqual(ObjectId("123456789012"), ObjectId("123456789012"))
-        self.assertNotEqual(ObjectId(), ObjectId())
-        self.assertNotEqual(ObjectId("123456789012"), "123456789012")
-
-    def test_new(self):
-        a = ObjectId()
-        b = ObjectId("123456789012")
-        self.assertTrue(a.is_new())
-        self.assertFalse(b.is_new())
-        a._use()
-        b._use()
-        self.assertFalse(a.is_new())
-        self.assertFalse(b.is_new())
-
-if __name__ == "__main__":
-    unittest.main()
diff --git a/test/test_objectid.py b/test/test_objectid.py
new file mode 100644
index 000000000..bd00fd154
--- /dev/null
+++ b/test/test_objectid.py
@@ -0,0 +1,48 @@
+"""Tests for the objectid module."""
+
+import unittest
+
+from objectid import ObjectId
+from errors import InvalidId
+
+class TestObjectId(unittest.TestCase):
+    def setUp(self):
+        pass
+
+    def test_creation(self):
+        self.assertRaises(TypeError, ObjectId, 4)
+        self.assertRaises(TypeError, ObjectId, u"hello")
+        self.assertRaises(TypeError, ObjectId, 175.0)
+        self.assertRaises(TypeError, ObjectId, {"test": 4})
+        self.assertRaises(TypeError, ObjectId, ["something"])
+        self.assertRaises(InvalidId, ObjectId, "")
+        self.assertRaises(InvalidId, ObjectId, "12345678901")
+        self.assertRaises(InvalidId, ObjectId, "1234567890123")
+        self.assertTrue(ObjectId())
+        self.assertTrue(ObjectId("123456789012"))
+        a = ObjectId()
+        self.assertTrue(ObjectId(a))
+
+    def test_repr_str(self):
+        self.assertEqual(repr(ObjectId("123456789012")), "ObjectId('123456789012')")
+        self.assertEqual(str(ObjectId("123456789012")), "123456789012")
+
+    def test_cmp(self):
+        a = ObjectId()
+        self.assertEqual(a, ObjectId(a))
+        self.assertEqual(ObjectId("123456789012"), ObjectId("123456789012"))
+        self.assertNotEqual(ObjectId(), ObjectId())
+        self.assertNotEqual(ObjectId("123456789012"), "123456789012")
+
+    def test_new(self):
+        a = ObjectId()
+        b = ObjectId("123456789012")
+        self.assertTrue(a.is_new())
+        self.assertFalse(b.is_new())
+        a._use()
+        b._use()
+        self.assertFalse(a.is_new())
+        self.assertFalse(b.is_new())
+
+if __name__ == "__main__":
+    unittest.main()