Add tests for default scope behaviour change

See #13875

activerecord/test/cases/scoping/default_scoping_test.rb

@@ -395,4 +395,22 @@ def test_default_scope_is_threadsafe
       threads.each(&:join)
     end
   end
+
+  test "additional conditions are ANDed with the default scope" do
+    scope = DeveloperCalledJamis.where(name: "David")
+    assert_equal 2, scope.where_values.length
+    assert_equal [], scope.to_a
+  end
+
+  test "additional conditions in a scope are ANDed with the default scope" do
+    scope = DeveloperCalledJamis.david
+    assert_equal 2, scope.where_values.length
+    assert_equal [], scope.to_a
+  end
+
+  test "a scope can remove the condition from the default scope" do
+    scope = DeveloperCalledJamis.david2
+    assert_equal 1, scope.where_values.length
+    assert_equal Developer.where(name: "David").map(&:id), scope.map(&:id)
+  end
 end

activerecord/test/models/developer.rb

@@ -165,6 +165,8 @@ class DeveloperCalledJamis < ActiveRecord::Base
 
   default_scope { where(:name => 'Jamis') }
   scope :poor, -> { where('salary < 150000') }
+  scope :david, -> { where name: "David" }
+  scope :david2, -> { unscoped.where name: "David" }
 end
 
 class PoorDeveloperCalledJamis < ActiveRecord::Base