Assertion for ensuring that two values are close enough within a certain threshold, comparing on the percentage difference

assert_close_enough.py

class SomeTestMixin:

    def assertCloseEnough(self, first, second, diff=0.0001):
        """
        Asserts that the percentage difference between the two values
        is smaller than given diff value.
        
        Results may depend on the order of the values. A more robust
        version might test the difference against both values.

        Args:
            first: original numerical argument
            second: comparison numerical argument
            diff: percentage difference allowed

        Returns:
            None

        Raises:
            AssertionError if the absolute % diff exceeds the diff threshold

        """
        if abs((first - second) / first) > diff:
            raise AssertionError("Difference between {f} and {s} is greater than {p}%".format(
                f=first,
                s=second,
                p=diff * 100,
            ))