test the number of times the schema is loading

activerecord/test/cases/schema_loading_test.rb

+require 'thread'
+require "cases/helper"
+
+module SchemaLoadCounter
+  extend ActiveSupport::Concern
+
+  module ClassMethods
+    attr_accessor :load_schema_calls
+
+    def load_schema!
+      self.load_schema_calls ||= 0
+      self.load_schema_calls +=1
+      super
+    end
+  end
+end
+
+class SchemaLoadingTest < ActiveRecord::TestCase
+  def test_basic_model_is_loaded_once
+    klass = define_model
+    klass.new
+    assert_equal 1, klass.load_schema_calls
+  end
+
+  def test_model_with_custom_lock_is_loaded_once
+    klass = define_model do |c|
+      c.table_name = :lock_without_defaults_cust
+      c.locking_column = :custom_lock_version
+    end
+    klass.new
+    assert_equal 1, klass.load_schema_calls
+  end
+
+  def test_model_with_changed_custom_lock_is_loaded_twice
+    klass = define_model do |c|
+      c.table_name = :lock_without_defaults_cust
+    end
+    klass.new
+    klass.locking_column = :custom_lock_version
+    klass.new
+    assert_equal 2, klass.load_schema_calls
+  end
+
+  private
+
+    def define_model
+      Class.new(ActiveRecord::Base) do
+        include SchemaLoadCounter
+        self.table_name = :lock_without_defaults
+        yield self if block_given?
+      end
+    end
+end