Allow defining the starting id for build_stubbed

Some codebases have long builds that create over 1000 records, and may
have id collisions between records created with FactoryBot.create and
FactoryBot.build_stubbed

Co-authored-by: Daniel Colson <danieljamescolson@gmail.com>

lib/factory_bot.rb

@@ -66,6 +66,15 @@ module FactoryBot
     Linter.new(factories_to_lint, **options).lint!
   end
 
+  # Set the starting value for ids when using the build_stubbed strategy
+  #
+  # Arguments:
+  # * starting_id +Integer+
+  #   The new starting id value.
+  def self.build_stubbed_starting_id=(starting_id)
+    Strategy::Stub.next_id = starting_id - 1
+  end
+
   class << self
     delegate :callback_names,
              :callbacks,

lib/factory_bot/strategy/stub.rb

@@ -24,6 +24,10 @@ module FactoryBot
         :update_columns,
       ].freeze
 
+      def self.next_id=(id)
+        @@next_id = id
+      end
+
       def association(runner)
         runner.run(:build_stubbed)
       end

spec/acceptance/build_stubbed_spec.rb

@@ -279,3 +279,21 @@ describe "defaulting `id`" do
     expect(FactoryBot.build_stubbed(:post, id: 12).id).to eq 12
   end
 end
+
+describe "configuring the starting id" do
+  it "defines which id build_stubbed instances start with" do
+    define_model("Post")
+
+    FactoryBot.define do
+      factory :post
+    end
+
+    FactoryBot.build_stubbed_starting_id = 1000
+
+    expect(FactoryBot.build_stubbed(:post).id).to eq 1000
+
+    FactoryBot.build_stubbed_starting_id = 3000
+
+    expect(FactoryBot.build_stubbed(:post).id).to eq 3000
+  end
+end