def read_inputs(fn):
    """Read guides and targets to test.

    Args:
        fn: path to TSV file; col 1 is target with context, col 2 is
            guide

    Returns:
         list of tuples (target with context, guide)
    """
    inputs = []
    with open(fn) as f:
        for line in f:
            line = line.rstrip()
            ls = line.split('\t')
            assert len(ls) == 2
            target_with_context, guide = ls

            if len(target_with_context) < len(guide):
                raise Exception(("Target with context is shorter than "
                    "guide in input"))

            inputs += [(target_with_context, guide)]
    return inputs