Small example demonstrating the need for testing functions with different types of input arguments. Here an integer division problem (in Python 2).

typetesting.py

from numpy import max, min


def mean_diff(a):
    """
    Parameters
    ----------
    a : array_like
    """
    return float((max(a) - min(a)) / (len(a) - 1))

def test_mean_diff():
    assert mean_diff([1., 7., 3., 2., 5.]) == 1.5 
    assert mean_diff([7, 3, 2, 1, 5]) == 1.5