Adding tests for ActiveModel::Model

* Verifying persisted? is false when Model initialized
* Passing nil to Model should not blow up
* Changing test name to the one suggested in pull request comment

activemodel/test/cases/model_test.rb

@@ -20,7 +20,13 @@ def test_initialize_with_params
   def test_initialize_with_nil_or_empty_hash_params_does_not_explode
     assert_nothing_raised do
       BasicModel.new()
+      BasicModel.new nil
       BasicModel.new({})
     end
   end
+
+  def test_persisted_is_always_false
+    object = BasicModel.new(:attr => "value")
+    assert object.persisted? == false
+  end
 end