Need to teardown the dynamically added method

test/action_controller/serialization_scope_name_test.rb

@@ -1,6 +1,19 @@
 require 'test_helper'
 
 module SerializationScopeTesting
+  def self.undef_serializer_dynamic_scope_methods
+      # @_serializer_instance_methods.include?(name) ||
+      #   @@_serializer_instance_methods[self].include?(name)
+    PostSerializer.send(:undef_method, :current_user) if PostSerializer.method_defined?(:current_user)
+    PostSerializer.send(:undef_method, :view_context) if PostSerializer.method_defined?(:view_context)
+    PostSerializer.instance_variable_get(:@_serializer_instance_methods).delete_if {|meth| [:current_user, :view_context].include?(meth) } rescue $!
+    PostSerializer.class_variable_get(:@@_serializer_instance_methods)[PostSerializer].delete_if {|meth| [:current_user, :view_context].include?(meth) } rescue $!
+
+    PostViewContextSerializer.send(:undef_method, :current_user) if PostViewContextSerializer.method_defined?(:current_user) rescue $!
+    PostViewContextSerializer.send(:undef_method, :view_context) if PostViewContextSerializer.method_defined?(:view_context) rescue $!
+    PostViewContextSerializer.instance_variable_get(:@_serializer_instance_methods).delete_if {|meth| [:current_user, :view_context].include?(meth) } rescue $!
+    PostViewContextSerializer.class_variable_get(:@@_serializer_instance_methods)[PostViewContextSerializer].delete_if {|meth| [:current_user, :view_context].include?(meth) } rescue $!
+  end
   class User < ActiveModelSerializers::Model
     attr_accessor :id, :name, :admin
     def admin?
@@ -70,6 +83,10 @@ def comments
   class DefaultScopeTest < ActionController::TestCase
     tests PostTestController
 
+    teardown do
+      SerializationScopeTesting.undef_serializer_dynamic_scope_methods
+    end
+
     def test_default_serialization_scope
       assert_equal :current_user, @controller._serialization_scope
     end
@@ -120,6 +137,10 @@ def serializer
     end
     tests PostViewContextTestController
 
+    teardown do
+      SerializationScopeTesting.undef_serializer_dynamic_scope_methods
+    end
+
     def test_defined_serialization_scope
       assert_equal :view_context, @controller._serialization_scope
     end
@@ -187,6 +208,10 @@ def new_post
     end
     tests PostViewContextTestController
 
+    teardown do
+      SerializationScopeTesting.undef_serializer_dynamic_scope_methods
+    end
+
     def test_nil_serialization_scope
       assert_nil @controller._serialization_scope
     end
@@ -225,18 +250,11 @@ def test_serialization_scope_is_and_nil_scope_passed_in_current_user
     end
 
     def test_serialization_scope_is_nil_and_scope_passed_in_current_user_without_scope_name
-      get :render_post_with_passed_in_scope_without_scope_name
-      expected_json = {
-        post: {
-          id: 4,
-          title: 'Title',
-          body: "The 'scope' is the 'current_user': true",
-          comments: [
-            { id: 2, body: 'Scoped' }
-          ]
-        }
-      }.to_json
-      assert_equal expected_json, @response.body
+      exception = assert_raises(NameError) do
+        get :render_post_with_passed_in_scope_without_scope_name
+      end
+      exception_matcher = /current_user/
+      assert_match exception_matcher, exception.message
     end
   end
 end