For integration tests use create and use a default test store with fixed ID to prevent issues when running parallel mutation tests.

ApplicationController queries for first_available_store_id that can result in differen workers being unable to find the record. Defailt test store is now shared between different mutant workers that should fix the problem.

Author: dysk

apps/rails_application/test/test_helper.rb

@@ -130,6 +130,8 @@ def payment_released
 end
 
 class InMemoryRESIntegrationTestCase < ActionDispatch::IntegrationTest
+  # Shared test store UUID - used by all parallel workers to avoid transaction isolation issues
+  DEFAULT_TEST_STORE_ID = "00000000-0000-4000-8000-000000000001"
 
   def before_setup
     result = super
@@ -139,7 +141,7 @@ def before_setup
     Rails.configuration.command_bus = Arkency::CommandBus.new
 
     Configuration.new.call(Rails.configuration.event_store, Rails.configuration.command_bus)
-    @default_store_id = register_store("Default Store")
+    @default_store_id = ensure_default_store
     result
   end
 
@@ -235,7 +237,22 @@ def run_command(command)
     Rails.configuration.command_bus.call(command)
   end
 
+  def ensure_default_store
+    # Create default test store directly in DB, outside of transaction
+    # This ensures it's visible to all parallel mutant workers
+    ActiveRecord::Base.connection.execute(<<-SQL)
+      INSERT INTO admin_stores (id, name, created_at, updated_at)
+      VALUES ('#{DEFAULT_TEST_STORE_ID}', 'Default Test Store', NOW(), NOW())
+      ON CONFLICT (id) DO NOTHING
+    SQL
+    DEFAULT_TEST_STORE_ID
+  end
+
   def register_store(name)
+    # For "Default Store", return the shared test store ID
+    return DEFAULT_TEST_STORE_ID if name == "Default Store" || name == "Default Test Store"
+
+    # For other stores, create normally
     store_id = SecureRandom.uuid
     post "/admin/stores", params: { store_id: store_id, name: name }
     store_id