Fix strategy tracking through associations

What?
=====

Within FactoryBot::Evaluator, the build strategy was reported either as
a class OR symbol.

A side-effect of this is misreporting within
ActiveSupport::Notifications hooks, since the instrumentation payload
may have strategies listed as e.g. `:create` or
`FactoryBot::Strategy::Create`, even though they semantically represent
the same information.

This introduces a new instance method for all strategies, `to_sym`,
to be called rather than `class`.

lib/factory_bot/evaluator.rb

@@ -24,7 +24,7 @@ module FactoryBot
     def association(factory_name, *traits_and_overrides)
       overrides = traits_and_overrides.extract_options!
       strategy_override = overrides.fetch(:strategy) {
-        FactoryBot.use_parent_strategy ? @build_strategy.class : :create
+        FactoryBot.use_parent_strategy ? @build_strategy.to_sym : :create
       }
 
       traits_and_overrides += [overrides.except(:strategy)]

lib/factory_bot/strategy/attributes_for.rb

@@ -8,6 +8,10 @@ module FactoryBot
       def result(evaluation)
         evaluation.hash
       end
+
+      def to_sym
+        :attributes_for
+      end
     end
   end
 end

lib/factory_bot/strategy/build.rb

@@ -10,6 +10,10 @@ module FactoryBot
           evaluation.notify(:after_build, instance)
         end
       end
+
+      def to_sym
+        :build
+      end
     end
   end
 end

lib/factory_bot/strategy/create.rb

@@ -13,6 +13,10 @@ module FactoryBot
           evaluation.notify(:after_create, instance)
         end
       end
+
+      def to_sym
+        :create
+      end
     end
   end
 end

lib/factory_bot/strategy/null.rb

@@ -6,6 +6,10 @@ module FactoryBot
 
       def result(evaluation)
       end
+
+      def to_sym
+        :null
+      end
     end
   end
 end

lib/factory_bot/strategy/stub.rb

@@ -41,6 +41,10 @@ module FactoryBot
         end
       end
 
+      def to_sym
+        :stub
+      end
+
       private
 
       def next_id

spec/acceptance/activesupport_instrumentation_spec.rb

@@ -16,6 +16,10 @@ describe "using ActiveSupport::Instrumentation to track factory interaction" do
   let(:user_factory) { FactoryBot::Internal.factory_by_name("user") }
   before do
     define_model("User", email: :string)
+    define_model("Post", user_id: :integer) do
+      belongs_to :user
+    end
+
     FactoryBot.define do
       factory :user do
         email { "john@example.com" }
@@ -24,6 +28,12 @@ describe "using ActiveSupport::Instrumentation to track factory interaction" do
           after(:build) { Kernel.sleep(0.1) }
         end
       end
+
+      factory :post do
+        trait :with_user do
+          user
+        end
+      end
     end
   end
 
@@ -55,6 +65,9 @@ describe "using ActiveSupport::Instrumentation to track factory interaction" do
       FactoryBot.build_list(:user, 5)
       FactoryBot.create_list(:user, 2)
       FactoryBot.attributes_for(:slow_user)
+      user = FactoryBot.create(:user)
+      FactoryBot.create(:post, user: user)
+      FactoryBot.create_list(:post, 2, :with_user)
     end
 
     expect(tracked_invocations[:slow_user][:build]).to eq(2)
@@ -62,5 +75,6 @@ describe "using ActiveSupport::Instrumentation to track factory interaction" do
     expect(tracked_invocations[:slow_user][:factory]).to eq(slow_user_factory)
     expect(tracked_invocations[:user][:build]).to eq(5)
     expect(tracked_invocations[:user][:factory]).to eq(user_factory)
+    expect(tracked_invocations[:user][:create]).to eq(5)
   end
 end