def add_suffix(in_files, suffix):
    """
    Wrap nipype's fname_presuffix to conveniently just add a prefix

    >>> add_suffix([
    ...     '/path/to/sub-045_ses-test_T1w.nii.gz',
    ...     '/path/to/sub-045_ses-retest_T1w.nii.gz'], '_test')
    'sub-045_ses-test_T1w_test.nii.gz'

    """
    import os.path as op
    from nipype.utils.filemanip import fname_presuffix, filename_to_list
    return op.basename(fname_presuffix(filename_to_list(in_files)[0],
        suffix=suffix))
