From a8dc787ff02490da17e8704ca564bf0c6b46c04d Mon Sep 17 00:00:00 2001
From: Mike Bayer <mike_mp@zzzcomputing.com>
Date: Tue, 6 Dec 2011 13:22:59 -0500
Subject: - [feature] IdentitySet supports the - operator as the same as
 difference(), handy when dealing with Session.dirty etc. [ticket:2301]

---
 test/base/test_utils.py | 13 +++++++++++++
 1 file changed, 13 insertions(+)

(limited to 'test/base/test_utils.py')

diff --git a/test/base/test_utils.py b/test/base/test_utils.py
index 61c7ad9d6..3a7ce07f2 100644
--- a/test/base/test_utils.py
+++ b/test/base/test_utils.py
@@ -290,6 +290,19 @@ class IdentitySetTest(fixtures.TestBase):
                 ids.add(data[i])
             self.assert_eq(ids, data)
 
+    def test_dunder_sub(self):
+        IdentitySet = util.IdentitySet
+        o1, o2, o3 = object(), object(), object()
+        ids1 = IdentitySet([o1])
+        ids2 = IdentitySet([o1, o2, o3])
+        eq_(
+            ids2 - ids1,
+            IdentitySet([o2, o3])
+        )
+        
+        ids2 -= ids1
+        eq_(ids2, IdentitySet([o2, o3]))
+
     def test_basic_sanity(self):
         IdentitySet = util.IdentitySet
 
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