individual tests should skip instead of failing if external apps not present

[nieder]

When running the tests, the entire test suite reports failure if a single test fails because an external dep (clustalw, mafft, uclust, etc) is not installed. Individual tests should first check if the required app is found, and only then execute. Otherwise, that specific test should be skipped.

[gregcaporaso]

PyNAST currently depends on Python 2.6, and conditional unit testing is only available in Python 2.7 and later. Going to delay this for now, as I don't want to change the dependency to 2.7 just for this.

[nieder]

Python is not yet my thing, but this was passed on to me by another member of the Fink team. Maybe it's helpful:

py27's unittest is available on py26 using unittest2-py26. Using it requires "import unittest2 as unittest"
http://www.voidspace.org.uk/python/articles/unittest2.shtml#test-skipping

And this snippet should make it work on all python versions:
try:
    import unittest2 as unittest
except ImportError:
    import unittest