1 files changed, 67 insertions, 0 deletions
diff --git a/activesupport/test/descendants_tracker_test_cases.rb b/activesupport/test/descendants_tracker_test_cases.rb
new file mode 100644
index 0000000000..2c94c3c56c
--- /dev/null
+++ b/activesupport/test/descendants_tracker_test_cases.rb
@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+require "set"
+
+module DescendantsTrackerTestCases
+  class Parent
+    extend ActiveSupport::DescendantsTracker
+  end
+
+  class Child1 < Parent
+  end
+
+  class Child2 < Parent
+  end
+
+  class Grandchild1 < Child1
+  end
+
+  class Grandchild2 < Child1
+  end
+
+  ALL = [Parent, Child1, Child2, Grandchild1, Grandchild2]
+
+  def test_descendants
+    assert_equal_sets [Child1, Grandchild1, Grandchild2, Child2], Parent.descendants
+    assert_equal_sets [Grandchild1, Grandchild2], Child1.descendants
+    assert_equal_sets [], Child2.descendants
+  end
+
+  def test_direct_descendants
+    assert_equal_sets [Child1, Child2], Parent.direct_descendants
+    assert_equal_sets [Grandchild1, Grandchild2], Child1.direct_descendants
+    assert_equal_sets [], Child2.direct_descendants
+  end
+
+  def test_clear
+    mark_as_autoloaded(*ALL) do
+      ActiveSupport::DescendantsTracker.clear
+      ALL.each do |k|
+        assert_empty ActiveSupport::DescendantsTracker.descendants(k)
+      end
+    end
+  end
+
+  private
+
+    def assert_equal_sets(expected, actual)
+      assert_equal Set.new(expected), Set.new(actual)
+    end
+
+    def mark_as_autoloaded(*klasses)
+      # If ActiveSupport::Dependencies is not loaded, forget about autoloading.
+      # This allows using AS::DescendantsTracker without AS::Dependencies.
+      if defined? ActiveSupport::Dependencies
+        old_autoloaded = ActiveSupport::Dependencies.autoloaded_constants.dup
+        ActiveSupport::Dependencies.autoloaded_constants = klasses.map(&:name)
+      end
+
+      old_descendants = ActiveSupport::DescendantsTracker.class_eval("@@direct_descendants").dup
+      old_descendants.each { |k, v| old_descendants[k] = v.dup }
+
+      yield
+    ensure
+      ActiveSupport::Dependencies.autoloaded_constants = old_autoloaded if defined? ActiveSupport::Dependencies
+      ActiveSupport::DescendantsTracker.class_eval("@@direct_descendants").replace(old_descendants)
+    end
+end