If the test was run before the YoutubeIE tests (for example by running
"nosetests -v test/test_compat.py test/test_download.py -m 'Youtube_1|compat_expand'"),
it wrote the signatures cache to the 'C:\Documents and Settings\тест\Application Data' folder.
It failed due to a problem in the cache code and the write_json_file function (fixed in f03e33b89a622af13fa5275c46b63aaa4814c499)
utils is large enough without these compatibility functions.
Everything that is present in newer versions of Python (i.e. with dev Python it's just an import) goes into compat.py .
Everything else (i.e. youtube-dl-specific helpers) goes into utils.py .
Sergey M․