Fix open_transactions_baseline to check the base class

We are querying the number of open transactions which is per connection,
so we have to do the same for the open_transactions_baseline

app/models/concerns/transactions.rb

@@ -8,7 +8,7 @@ module Transactions
     # transaction. Handles special cases when running inside a test environment,
     # where tests may be wrapped in transactions
     def inside_transaction?
-      base = Rails.env.test? ? @open_transactions_baseline.to_i : 0
+      base = Rails.env.test? ? open_transactions_baseline.to_i : 0
 
       connection.open_transactions > base
     end
@@ -24,5 +24,15 @@ module Transactions
     def reset_open_transactions_baseline
       @open_transactions_baseline = 0
     end
+
+    def open_transactions_baseline
+      return unless Rails.env.test?
+
+      if @open_transactions_baseline.nil?
+        return self == ApplicationRecord ? nil : superclass.open_transactions_baseline
+      end
+
+      @open_transactions_baseline
+    end
   end
 end

spec/models/concerns/transactions_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Transactions do
+  let(:model) { build(:project) }
+
+  it 'is not in a transaction' do
+    expect(model.class).not_to be_inside_transaction
+  end
+
+  it 'is in a transaction', :aggregate_failures do
+    Project.transaction do
+      expect(model.class).to be_inside_transaction
+    end
+
+    ApplicationRecord.transaction do
+      expect(model.class).to be_inside_transaction
+    end
+  end
+end