Objects that compare equal automatically pass or fail assertAlmostEqual and…

Objects that compare equal automatically pass or fail assertAlmostEqual and assertNotAlmostEqual tests on unittest.TestCase. Issue 6567.

Doc/library/unittest.rst

@@ -733,6 +733,9 @@ Test cases
       compare equal, the test will fail with the explanation given by *msg*, or
       :const:`None`.
 
+      .. versionchanged:: 2.7
+         Objects that compare equal are automatically almost equal.
+
       .. deprecated:: 2.7
          :meth:`failUnlessAlmostEqual`.
 
@@ -749,6 +752,9 @@ Test cases
       compare equal, the test will fail with the explanation given by *msg*, or
       :const:`None`.
 
+      .. versionchanged:: 2.7
+         Objects that compare equal automatically fail.
+
       .. deprecated:: 2.7
          :meth:`failIfAlmostEqual`.
 

Doc/whatsnew/2.7.rst

@@ -505,6 +505,10 @@ changes, or look through the Subversion logs for all the details.
     differences.  :meth:`assertDictContainsSubset` checks whether
     all of the key/value pairs in *first* are found in *second*.
 
+  * :meth:`assertAlmostEqual` and :meth:`assertNotAlmostEqual` short-circuit
+    (automatically pass or fail without checking decimal places) if the objects
+    are equal.
+
   * A new hook, :meth:`addTypeEqualityFunc` takes a type object and a
     function.  The :meth:`assertEqual` method will use the function
     when both of the objects being compared are of the specified type.

Lib/test/test_unittest.py

@@ -2989,6 +2989,11 @@ class Test_Assertions(TestCase):
         self.assertRaises(self.failureException,
                           self.assertNotAlmostEqual, 0, .1+.1j, places=0)
 
+        self.assertAlmostEqual(float('inf'), float('inf'))
+        self.assertRaises(self.failureException, self.assertNotAlmostEqual,
+                          float('inf'), float('inf'))
+
+
     def test_assertRaises(self):
         def _raise(e):
             raise e

Lib/unittest/case.py

@@ -457,7 +457,13 @@ class TestCase(object):
 
            Note that decimal places (from zero) are usually not the same
            as significant digits (measured from the most signficant digit).
+
+           If the two objects compare equal then they will automatically
+           compare almost equal.
         """
+        if first == second:
+            # shortcut for ite
+            return
         if round(abs(second-first), places) != 0:
             standardMsg = '%r != %r within %r places' % (first, second, places)
             msg = self._formatMessage(msg, standardMsg)
@@ -470,8 +476,10 @@ class TestCase(object):
 
            Note that decimal places (from zero) are usually not the same
            as significant digits (measured from the most signficant digit).
+
+           Objects that are equal automatically fail.
         """
-        if round(abs(second-first), places) == 0:
+        if (first == second) or round(abs(second-first), places) == 0:
             standardMsg = '%r == %r within %r places' % (first, second, places)
             msg = self._formatMessage(msg, standardMsg)
             raise self.failureException(msg)