Hola!
I noticed something very strange in unit tests for /languages/Language.php (/tests/phpunit/languages/LanguageTest.php):
Language::sprintfDate() is tested to conform with expected formatted date strings. In the test file method 'provideSprintfDateSamples' provides a test case for the format bit 'W' which means "ISO 8601 week number, zero-padded". Language::sprintfDate() outputs the result for W as documented. However, one of the test cases for this format contains expected value "1" (instead of "01"). As I said above, sprintfDate() adds a zero (printing "01"), but when I run the tests, they just pass!
What is wrong here? Wrong test case + issue in PHPUnit or what?