Better error for trying to mock builtins

flexmock.py

@@ -32,6 +32,13 @@ class FlexmockException(Exception):
   pass
 
 
+class AttemptingToMockBuiltin(Exception):
+  def __str__(self):
+    out = 'Python does not allow you to mock builtin modules. '
+    out += 'Consider wrapping it in a class you can mock instead'
+    return out
+
+
 class InvalidMethodSignature(FlexmockException):
   pass
 
@@ -636,6 +643,8 @@ def _generate_mock(flexmock_class, object_or_class=None, **kwargs):
     mock = flexmock_class()
     try:
       mock._setup_mock(object_or_class, **kwargs)
+    except TypeError:
+      raise AttemptingToMockBuiltin
     except AlreadyMocked:
       mock = object_or_class
   return mock

flexmock_test.py

@@ -2,6 +2,7 @@
 from flexmock import FlexMock
 from flexmock import AlreadyMocked
 from flexmock import AndExecuteNotSupportedForClassMocks
+from flexmock import AttemptingToMockBuiltin
 from flexmock import Expectation
 from flexmock import FlexmockContainer
 from flexmock import FlexmockException
@@ -804,7 +805,6 @@ class User: pass
     mock = flexmock(user)
     try:
       flexmock(user).should_receive('nonexistent')
-      assert False
     except MethodDoesNotExist:
       assert True
       return
@@ -820,6 +820,14 @@ def test_flexmock_should_not_explode_on_unicode_formatting(self):
           'method', {'kargs' : (unichr(0x86C7),), 'kwargs' : {}})
       assert formatted == 'method("%s")' % unichr(0x86C7)
 
+  def test_flexmock_should_give_reasonable_error_for_builtins(self):
+    try:
+      flexmock(object).should_receive('time')
+    except AttemptingToMockBuiltin:
+      assert True
+      return
+    assert False
+
 
 if __name__ == '__main__':
   unittest.main()

run_tests.sh

@@ -12,6 +12,6 @@ done
 if test -f "$(which nosetests)"; then
 	echo nosetests
 	nosetests flexmock_test.py
-echo
+else
 	echo nosetests NOT FOUND
 fi