Eagerly materialize the fixtures transaction

activerecord/lib/active_record/connection_adapters/abstract/transaction.rb

@@ -205,9 +205,12 @@ def begin_transaction(options = {})
                                        run_commit_callbacks: run_commit_callbacks)
             end
 
-          transaction.materialize! unless @connection.supports_lazy_transactions? && lazy_transactions_enabled?
+          if @connection.supports_lazy_transactions? && lazy_transactions_enabled? && options[:_lazy] != false
+            @has_unmaterialized_transactions = true
+          else
+            transaction.materialize!
+          end
           @stack.push(transaction)
-          @has_unmaterialized_transactions = true if @connection.supports_lazy_transactions?
           transaction
         end
       end

activerecord/lib/active_record/test_fixtures.rb

@@ -122,7 +122,7 @@ def setup_fixtures(config = ActiveRecord::Base)
         # Begin transactions for connections already established
         @fixture_connections = enlist_fixture_connections
         @fixture_connections.each do |connection|
-          connection.begin_transaction joinable: false
+          connection.begin_transaction joinable: false, _lazy: false
           connection.pool.lock_thread = true if lock_threads
         end
 
@@ -138,7 +138,7 @@ def setup_fixtures(config = ActiveRecord::Base)
             end
 
             if connection && !@fixture_connections.include?(connection)
-              connection.begin_transaction joinable: false
+              connection.begin_transaction joinable: false, _lazy: false
               connection.pool.lock_thread = true if lock_threads
               @fixture_connections << connection
             end

activerecord/test/cases/fixtures_test.rb

@@ -924,7 +924,7 @@ def rollback_transaction(*args); end
       def lock_thread=(lock_thread); end
     end.new
 
-    assert_called_with(connection, :begin_transaction, [joinable: false]) do
+    assert_called_with(connection, :begin_transaction, [joinable: false, _lazy: false]) do
       fire_connection_notification(connection)
     end
   end