Execute FactoryBot.lint! in database transactions (#1726)

Prior to this change `FactoryBot.lint!` execution can trigger sequential
`FactoryBot.create` calls made within the same test (either Minitest
`test` or RSpec `it` blocks).

This can result in linting violations for records that have
database-level uniqueness constraints.

This commit introduces the private `Linter#in_transaction` method to
wrap the executing block within an [ActiveRecord::Base.transaction][]
block that concludes with raising an [ActiveRecord::Rollback][] error.

After this change, executions no longer contest with database-level
uniqueness constraints.

[ActiveRecord::Base.transaction]: https://edgeapi.rubyonrails.org/classes/ActiveRecord/Transactions/ClassMethods.html#method-i-transaction
[ActiveRecord::Rollback]: https://edgeapi.rubyonrails.org/classes/ActiveRecord/Rollback.html

Author: seanpdoyle

NEWS.md

@@ -1,5 +1,9 @@
 # News
 
+## Unreleased
+
+  * Changed: execute linting tests within ActiveRecord transactions when available
+
 ## 6.5.0 (September 6, 2024)
 
   * fix: issue 1621 broken links in ref/factory.md by @elasticspoon in https://github.com/thoughtbot/factory_bot/pull/1623

lib/factory_bot/linter.rb

@@ -70,7 +70,7 @@ def lint(factory)
     def lint_factory(factory)
       result = []
       begin
-        FactoryBot.public_send(factory_strategy, factory.name)
+        in_transaction { FactoryBot.public_send(factory_strategy, factory.name) }
       rescue => e
         result |= [FactoryError.new(e, factory)]
       end
@@ -80,7 +80,7 @@ def lint_factory(factory)
     def lint_traits(factory)
       result = []
       factory.definition.defined_traits.map(&:name).each do |trait_name|
-        FactoryBot.public_send(factory_strategy, factory.name, trait_name)
+        in_transaction { FactoryBot.public_send(factory_strategy, factory.name, trait_name) }
       rescue => e
         result |= [FactoryTraitError.new(e, factory, trait_name)]
       end
@@ -106,5 +106,16 @@ def error_message_type
         :message
       end
     end
+
+    def in_transaction
+      if defined?(ActiveRecord::Base)
+        ActiveRecord::Base.transaction do
+          yield
+          raise ActiveRecord::Rollback
+        end
+      else
+        yield
+      end
+    end
   end
 end

spec/acceptance/lint_spec.rb

@@ -26,6 +26,24 @@
     }.to raise_error FactoryBot::InvalidFactoryError, error_message
   end
 
+  it "executes linting in an ActiveRecord::Base transaction" do
+    define_model "User", name: :string do
+      validates :name, uniqueness: true
+    end
+
+    define_model "AlwaysValid"
+
+    FactoryBot.define do
+      factory :user do
+        factory :admin_user
+      end
+
+      factory :always_valid
+    end
+
+    expect { FactoryBot.lint }.to_not raise_error
+  end
+
   it "does not raise when all factories are valid" do
     define_model "User", name: :string do
       validates :name, presence: true