Update difference behavior to support NaN values inside tuples.

datatest/differences.py

@@ -31,11 +31,17 @@
 )
 
 
-def _nan_to_token(x):
-    with suppress(TypeError):
-        if isnan(x):
-            return NANTOKEN
-    return x
+def _nan_to_token(value):
+    """Return NANTOKEN if *value* is NaN else return value unchanged."""
+    def func(x):
+        with suppress(TypeError):
+            if isnan(x):
+                return NANTOKEN
+        return x
+
+    if isinstance(value, tuple):
+        return tuple(func(x) for x in value)
+    return func(value)
 
 
 class BaseDifference(abc.ABC):

tests/test_difference.py

@@ -85,6 +85,11 @@ def test_nan_equal(self):
         second = MinimalDifference(float('nan'))
         self.assertEqual(first, second)
 
+        # NaNs nested in a tuple should also test as equal.
+        first = MinimalDifference(('abc', float('nan')))
+        second = MinimalDifference(('abc', float('nan')))
+        self.assertEqual(first, second)
+
     def test_comparing_different_types(self):
         diff = MinimalDifference('X')
         self.assertNotEqual(diff, Exception('X'))