Round a value to an integer [1-9] times a power of 10. How would you write a test for this method?

round_exponential.py

import numpy as np

def round_exponential(val):
    """
    Round a value to an integer [1-9] times a power of 10.

    Example
    >>> val1 = 7.83126342297e-07
    >>> print round_exponential(val1)
    >>> 8e-07
    >>> val2 = -6.9322190125e+13
    >>> print round_exponential(val2) 
    >>> -7e+13
    """
    expt = np.floor(np.log10(np.abs(val)))
    mant = val / 10**expt
    return np.round(mant) * 10**expt

I'd just have it test your few examples.