#403 fix testing pygments dependency

[Chris Sewell]

I don't believe, there is any mention that pygments is a requirement for tests to pass.
But if not functional/tests/latex_memoir.py fails with many diffs
Even then, installing the latest pygments leads to a minor diff: https://github.com/chrisjsewell/docutils/commit/a933b1c57467f5f337d9d718a04e6624e927b7b7
So I'm not sure if only a specific version is supported?

[Takeshi KOMIYA]

I don't know about dependencies. But, about the diff, it seems the reason of diff comes python versions. The "print" is a keyword in python2 era. But it becomes a mere function since python3. So it becomes a name now. I guess it might go well if you invoke a testcase with python2.

Anyway, checking the output of pygments is too fragile. It often gets broken everytime pygments changes the highlighting rule. It is better to check only that the content is highlighted.

[engelbert gruber]

i only have test failures in functional/tests/latex_memoir.py lately
any other place ?

[engelbert gruber]

disabled in _default.py

settings_overrides['syntax_highlight'] = 'none'

syntax highlighting is tested in test/test_parsers/test_rst/test_directives/test_code_long.py