Correctly teardown test case, avoid filehandle leaking.

IPython/testing/iptest.py

@@ -44,6 +44,8 b' pjoin = path.join'
 
 
 # Enable printing all warnings raise by IPython's modules
+if sys.version_info > (3,0):
+    warnings.filterwarnings('error', message='.*', category=ResourceWarning, module='.*')
 warnings.filterwarnings('default', message='.*', category=Warning, module='IPy.*')
 
 if version_info < (6,):

IPython/testing/tests/test_tools.py

@@ -132,3 +132,9 b' class Test_ipexec_validate(unittest.TestCase, tt.TempFileMixin):'
                    )
         out = "A\r\nB"
         tt.ipexec_validate(self.fname, expected_out=out, expected_err="C\r\nD")
+
+
+    def tearDown(self):
+        # tear down correctly the mixin,
+        # unittest.TestCase.tearDown does nothing
+        tt.TempFileMixin.tearDown(self)