How to check if value is nan in unittest?

Question

I’ve got functions, which sometimes return NaNs with float('nan') (I’m not using numpy).

How do I write a test for it, since

assertEqual(nan_value, float('nan'))

is just like float('nan') == float('nan') always false. Is there maybe something like assertIsNan? I could not find anything about it…

Asked By: tamasgal

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Source

Answer 1

I came up with

assertTrue(math.isnan(nan_value))

Answered By: tamasgal

Answer 2

math.isnan(x) will raise a TypeError if x is neither a float nor a Real.

It’s better to use something like this :

import math


class NumericAssertions:
    """
    This class is following the UnitTest naming conventions.
    It is meant to be used along with unittest.TestCase like so :
    class MyTest(unittest.TestCase, NumericAssertions):
        ...
    It needs python >= 2.6
    """

    def assertIsNaN(self, value, msg=None):
        """
        Fail if provided value is not NaN
        """
        standardMsg = "%s is not NaN" % str(value)
        try:
            if not math.isnan(value):
                self.fail(self._formatMessage(msg, standardMsg))
        except:
            self.fail(self._formatMessage(msg, standardMsg))

    def assertIsNotNaN(self, value, msg=None):
        """
        Fail if provided value is NaN
        """
        standardMsg = "Provided value is NaN"
        try:
            if math.isnan(value):
                self.fail(self._formatMessage(msg, standardMsg))
        except:
            pass

You can then use self.assertIsNaN() and self.assertIsNotNaN().

Answered By: LaGoutte

Answer 3

Update with NumPy: I know the OP is not using numpy. However, I had to use numpy and didn’t find any post. So I’ll leave the answer here for anybody that may need help. It also works perfectly with unittest library.

import numpy as np
np.testing.assert_equal(nan_value, np.nan)

Answered By: user3503711

Answer 4

Keying off of @user3503711’s answer, the following worked for me:

numpy.isnan(nan_value)

I am using numpy==1.22.2. See https://numpy.org/doc/1.22/reference/generated/numpy.isnan.html

Answered By: dirtyqwerty

How to check if value is nan in unittest?

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