1 files changed, 19 insertions, 0 deletions
diff --git a/test/test_set.rb b/test/test_set.rb
index 9439974fea..07c404ab79 100644
--- a/test/test_set.rb
+++ b/test/test_set.rb
@@ -715,6 +715,25 @@ class TC_Set < Test::Unit::TestCase
     set1.add(set2)
     assert_equal(true, set1.inspect.include?('#<Set: {...}>'))
   end
+
+  def test_compare_by_identity
+    a1, a2 = "a", "a"
+    b1, b2 = "b", "b"
+    c = "c"
+    array = [a1, b1, c, a2, b2]
+
+    iset = Set.new.compare_by_identity
+    assert_send([iset, :compare_by_identity?])
+    iset.merge(array)
+    assert_equal(5, iset.size)
+    assert_equal(array.map(&:object_id).sort, iset.map(&:object_id).sort)
+
+    set = Set.new
+    assert_not_send([set, :compare_by_identity?])
+    set.merge(array)
+    assert_equal(3, set.size)
+    assert_equal(array.uniq.sort, set.sort)
+  end
 end
 
 class TC_SortedSet < Test::Unit::TestCase