fix tests to run without the MySQLdb driver installed

tests/run_test.py

@@ -3,7 +3,7 @@
 import os
 import sys
 from StringIO import StringIO
-from mock import patch, Mock
+from mock import patch, Mock, MagicMock
 
 class RunTest(unittest.TestCase):
 
@@ -233,6 +233,7 @@ def test_it_should_check_if_has_a_default_configuration_file(self, main_mock, ex
         self.assertTrue(isinstance(config_used, simple_db_migrate.config.FileConfig))
         self.assertEqual('host_on_sample_configuration_filename', config_used.get('database_host'))
 
+    @patch.dict('sys.modules', MySQLdb=MagicMock())
     @patch.object(simple_db_migrate.main.Main, 'labels', return_value=["v1", "foo", "v3"])
     def test_it_should_print_labels_on_database_and_exit(self, labels_mock):
         try:
@@ -242,6 +243,7 @@ def test_it_should_print_labels_on_database_and_exit(self, labels_mock):
 
         self.assertEqual('v1\nfoo\nv3\n\n', sys.stdout.getvalue())
 
+    @patch.dict('sys.modules', MySQLdb=MagicMock())
     @patch.object(simple_db_migrate.main.Main, 'labels', return_value=[])
     def test_it_should_print_none_when_there_are_no_labels_on_database_and_exit(self, labels_mock):
         try:
@@ -251,6 +253,7 @@ def test_it_should_print_none_when_there_are_no_labels_on_database_and_exit(self
 
         self.assertEqual('NONE\n\n', sys.stdout.getvalue())
 
+    @patch.dict('sys.modules', MySQLdb=MagicMock())
     @patch.object(simple_db_migrate.main.Main, 'last_label', return_value="v3")
     def test_it_should_print_last_label_on_database_and_exit(self, last_label_mock):
         try:
@@ -260,6 +263,7 @@ def test_it_should_print_last_label_on_database_and_exit(self, last_label_mock):
 
         self.assertEqual('v3\n\n', sys.stdout.getvalue())
 
+    @patch.dict('sys.modules', MySQLdb=MagicMock())
     @patch.object(simple_db_migrate.main.Main, 'last_label', return_value=None)
     def test_it_should_print_none_as_last_label_when_there_are_no_labels_on_database_and_exit(self, last_label_mock):
         try:
@@ -269,6 +273,7 @@ def test_it_should_print_none_as_last_label_when_there_are_no_labels_on_database
 
         self.assertEqual('NONE\n\n', sys.stdout.getvalue())
 
+    @patch.dict('sys.modules', MySQLdb=MagicMock())
     def test_it_should_print_error_message_and_exit_when_required_info_is_not_valid(self):
         try:
             simple_db_migrate.run_from_argv(["--info", "not_valid", "-c", os.path.abspath('sample.conf')])