3 files changed, 50 insertions, 6 deletions
diff --git a/actionpack/test/controller/parameters/dup_test.rb b/actionpack/test/controller/parameters/dup_test.rb
new file mode 100644
index 0000000000..66bc8155c8
--- /dev/null
+++ b/actionpack/test/controller/parameters/dup_test.rb
@@ -0,0 +1,43 @@
+require 'abstract_unit'
+require 'action_controller/metal/strong_parameters'
+
+class ParametersDupTest < ActiveSupport::TestCase
+  setup do
+    ActionController::Parameters.permit_all_parameters = false
+
+    @params = ActionController::Parameters.new(
+      person: {
+        age: '32',
+        name: {
+          first: 'David',
+          last: 'Heinemeier Hansson'
+        },
+        addresses: [{city: 'Chicago', state: 'Illinois'}]
+      }
+    )
+  end
+
+  test "a duplicate maintains the original's permitted status" do
+    @params.permit!
+    dupped_params = @params.dup
+    assert dupped_params.permitted?
+  end
+
+  test "a duplicate maintains the original's parameters" do
+    @params.permit!
+    dupped_params = @params.dup
+    assert_equal @params.to_h, dupped_params.to_h
+  end
+
+  test "changes to a duplicate's parameters do not affect the original" do
+    dupped_params = @params.dup
+    dupped_params.delete(:person)
+    assert_not_equal @params, dupped_params
+  end
+
+  test "changes to a duplicate's permitted status do not affect the original" do
+    dupped_params = @params.dup
+    dupped_params.permit!
+    assert_not_equal @params, dupped_params
+  end
+end
diff --git a/actionpack/test/controller/parameters/nested_parameters_test.rb b/actionpack/test/controller/parameters/nested_parameters_permit_test.rb
index 7151a8567c..5cf6f0d4e8 100644
--- a/actionpack/test/controller/parameters/nested_parameters_test.rb
+++ b/actionpack/test/controller/parameters/nested_parameters_permit_test.rb
@@ -1,7 +1,7 @@
 require 'abstract_unit'
 require 'action_controller/metal/strong_parameters'
 
-class NestedParametersTest < ActiveSupport::TestCase
+class NestedParametersPermitTest < ActiveSupport::TestCase
   def assert_filtered_out(params, key)
     assert !params.has_key?(key), "key #{key.inspect} has not been filtered out"
   end
diff --git a/actionpack/test/controller/parameters/parameters_permit_test.rb b/actionpack/test/controller/parameters/parameters_permit_test.rb
index b75eb0e3bf..2dd94c7230 100644
--- a/actionpack/test/controller/parameters/parameters_permit_test.rb
+++ b/actionpack/test/controller/parameters/parameters_permit_test.rb
@@ -245,11 +245,6 @@ class ParametersPermitTest < ActiveSupport::TestCase
     assert_equal "Jonas", @params[:person][:family][:brother]
   end
 
-  test "permit state is kept on a dup" do
-    @params.permit!
-    assert_equal @params.permitted?, @params.dup.permitted?
-  end
-
   test "permit is recursive" do
     @params.permit!
     assert @params.permitted?
@@ -369,4 +364,10 @@ class ParametersPermitTest < ActiveSupport::TestCase
     refute params.permit(foo: [:bar]).has_key?(:foo)
     refute params.permit(foo: :bar).has_key?(:foo)
   end
+
+  test '#permitted? is false by default' do
+    params = ActionController::Parameters.new
+
+    assert_equal false, params.permitted?
+  end
 end