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pythonunit-testingassertnan
tamasgal
tamasgal

Reputation: 26259

How to check if value is nan in unittest?

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…

Upvotes: 37

Views: 19766

Answers (4)

dirtyqwerty
dirtyqwerty

Reputation: 305

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

Upvotes: 2

user3503711
user3503711

Reputation: 2066

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)

Upvotes: 6

LaGoutte
LaGoutte

Reputation: 468

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().

Upvotes: 13

tamasgal
tamasgal

Reputation: 26259

I came up with

assertTrue(math.isnan(nan_value))

Upvotes: 40

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