Formats: Use real filename for tests

Otherwise some formats might not be working properly.

Issue #1525

Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/formats/tests/test_formats.py

@@ -174,7 +174,7 @@ def test_save(self, edit=False):
             testdata = handle.read()
 
         # Create test file
-        testfile = os.path.join(self.tempdir, 'test.{0}'.format(self.EXT))
+        testfile = os.path.join(self.tempdir, os.path.basename(self.FILE))
 
         # Write test data to file
         with open(testfile, 'wb') as handle: