1 files changed, 40 insertions, 0 deletions
diff --git a/activesupport/test/core_ext/class_test.rb b/activesupport/test/core_ext/class_test.rb
new file mode 100644
index 0000000000..5ea288738e
--- /dev/null
+++ b/activesupport/test/core_ext/class_test.rb
@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+require "abstract_unit"
+require "active_support/core_ext/class"
+require "set"
+
+class ClassTest < ActiveSupport::TestCase
+  class Parent; end
+  class Foo < Parent; end
+  class Bar < Foo; end
+  class Baz < Bar; end
+
+  class A < Parent; end
+  class B < A; end
+  class C < B; end
+
+  def test_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].to_set, Parent.subclasses.to_set
+    assert_equal [Bar], Foo.subclasses
+    assert_equal [Baz], Bar.subclasses
+    assert_equal [], Baz.subclasses
+  end
+
+  def test_descendants_excludes_singleton_classes
+    klass = Parent.new.singleton_class
+    assert_not Parent.descendants.include?(klass), "descendants should not include singleton classes"
+  end
+
+  def test_subclasses_excludes_singleton_classes
+    klass = Parent.new.singleton_class
+    assert_not Parent.subclasses.include?(klass), "subclasses should not include singleton classes"
+  end
+end