Don't rely on implementation-specific order-dependence of array comparisons in unit tests

Signed-off-by: NSantiago Pastorino <santiago@wyeworks.com>

activesupport/test/core_ext/class_test.rb

 require 'abstract_unit'
 require 'active_support/core_ext/class'
+require 'set'
 
 class ClassTest < Test::Unit::TestCase
   class Parent; end
@@ -12,16 +13,16 @@ class B < A; end
   class C < B; end
 
   def test_descendants
-    assert_equal [Foo, Bar, Baz, A, B, C], Parent.descendants
-    assert_equal [Bar, Baz], Foo.descendants
+    assert_equal [Foo, Bar, Baz, A, B, C].to_set, Parent.descendants.to_set
+    assert_equal [Bar, Baz].to_set, Foo.descendants.to_set
     assert_equal [Baz], Bar.descendants
     assert_equal [], Baz.descendants
   end
 
   def test_subclasses
-    assert_equal [Foo, A], Parent.subclasses
+    assert_equal [Foo, A].to_set, Parent.subclasses.to_set
     assert_equal [Bar], Foo.subclasses
     assert_equal [Baz], Bar.subclasses
     assert_equal [], Baz.subclasses
   end
-end
\ No newline at end of file
+end