test runner: close files immediately after use

runtests.py

@@ -316,6 +316,7 @@ class CythonCompileTestCase(unittest.TestCase):
         source_file = os.path.join(test_directory, module) + '.pyx'
         source_and_output = codecs.open(
             self.find_module_source_file(source_file), 'rU', 'ISO-8859-1')
+        try:
             out = codecs.open(os.path.join(workdir, module + '.pyx'),
                               'w', 'ISO-8859-1')
             for line in source_and_output:
@@ -325,9 +326,12 @@ class CythonCompileTestCase(unittest.TestCase):
                     out = ErrorWriter()
                 else:
                     out.write(line)
+        finally:
+            source_and_output.close()
         try:
             geterrors = out.geterrors
         except AttributeError:
+            out.close()
             return []
         else:
             return geterrors()