[test_download]: -m regexp to run matching tests

Run test modules whose name matches the given regexp.
This is quick-and-dirty, there's probably a better way,
but the TestSuite system is really complicated and this is
super-easy.

README.md

@@ -987,7 +987,7 @@ After you have ensured this site is distributing it's content legally, you can f
             }
     ```
 5. Add an import in [`youtube_dl/extractor/extractors.py`](https://github.com/rg3/youtube-dl/blob/master/youtube_dl/extractor/extractors.py).
-6. Run `python test/test_download.py TestDownload.test_YourExtractor`. This *should fail* at first, but you can continually re-run it until you're done. If you decide to add more than one test, then rename ``_TEST`` to ``_TESTS`` and make it into a list of dictionaries. The tests will then be named `TestDownload.test_YourExtractor`, `TestDownload.test_YourExtractor_1`, `TestDownload.test_YourExtractor_2`, etc.
+6. Run `python test/test_download.py -m YourExtractor` to run all tests for YourExtractor. This *should fail* at first, but you can continually re-run it until you're done. If you decide to add more than one test, then rename ``_TEST`` to ``_TESTS`` and make it into a list of dictionaries. The tests will then be named `TestDownload.test_YourExtractor`, `TestDownload.test_YourExtractor_1`, `TestDownload.test_YourExtractor_2`, etc. You run individual tests with `python test/test_download.py TestDownload.test_YourExtractor`, etc.
 7. Have a look at [`youtube_dl/extractor/common.py`](https://github.com/rg3/youtube-dl/blob/master/youtube_dl/extractor/common.py) for possible helper methods and a [detailed description of what your extractor should and may return](https://github.com/rg3/youtube-dl/blob/master/youtube_dl/extractor/common.py#L74-L252). Add tests and code for as many as you want.
 8. Make sure your code follows [youtube-dl coding conventions](#youtube-dl-coding-conventions) and check the code with [flake8](https://pypi.python.org/pypi/flake8). Also make sure your code works under all [Python](http://www.python.org/) versions claimed supported by youtube-dl, namely 2.6, 2.7, and 3.2+.
 9. When the tests pass, [add](http://git-scm.com/docs/git-add) the new files and [commit](http://git-scm.com/docs/git-commit) them and [push](http://git-scm.com/docs/git-push) the result, like this:

test/test_download.py

@@ -4,6 +4,7 @@ from __future__ import unicode_literals
 
 # Allow direct execution
 import os
+import re
 import sys
 import unittest
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
@@ -217,18 +218,28 @@ def generator(test_case):
 
     return test_template
 
+module = ""
+if __name__ == '__main__':
+    import sys
+    if len(sys.argv)>2 and sys.argv[1] == '-m':
+        module = sys.argv[2]
+        del sys.argv[2], sys.argv[1]
+
 # And add them to TestDownload
 for n, test_case in enumerate(defs):
     test_method = generator(test_case)
+    if not re.match(module, test_case['name']):
+        continue
     tname = 'test_' + str(test_case['name'])
+
     i = 1
     while hasattr(TestDownload, tname):
         tname = 'test_%s_%d' % (test_case['name'], i)
         i += 1
     test_method.__name__ = str(tname)
     setattr(TestDownload, test_method.__name__, test_method)
-    del test_method
 
+    del test_method
 
 if __name__ == '__main__':
     unittest.main()