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…

Answer 1

I came up with

assertTrue(math.isnan(nan_value)) 

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().