STY: refactor IGMM tests
STY: refactor IGMM tests

Replace assert with assert_true, assert_array_equal
Whitespace, PEP 8
Docstrings to comments
Fix some typos
Remove print statements

alexis-roche/niseg,arokem/nipy,alexis-roche/niseg,alexis-roche/nipy,nipy/nipy-labs,bthirion/nipy,nipy/nipy-labs,alexis-roche/register,bthirion/nipy,alexis-roche/nipy,alexis-roche/register,bthirion/nipy,arokem/nipy,bthirion/nipy,nipy/nireg,alexis-roche/nipy,arokem/nipy,alexis-roche/nireg,alexis-roche/nipy,alexis-roche/register,alexis-roche/nireg,arokem/nipy,nipy/nireg