Decouple test models from ActiveRecord

Intention is to allow testing multiple ORMs more easily, with equivalent
data.

Author: ellnix

spec/spec_helper.rb

@@ -44,6 +44,7 @@
 NEW_RAILS = Gem.loaded_specs['rails'].version >= Gem::Version.new('6.0')
 
 Dir["#{File.dirname(__FILE__)}/support/*.rb"].each { |file| require file }
+Dir["#{File.dirname(__FILE__)}/support/test_models/*.rb"].each { |file| require file }
 
 RSpec.configure do |c|
   c.mock_with :rspec

spec/support/3_model_specification.rb

@@ -0,0 +1,13 @@
+module Models
+  class ModelSpecification
+    Field = Data.define(:name, :type)
+
+    attr_reader :name, :fields, :body
+
+    def initialize(klass_name, fields:, &block)
+      @name = klass_name
+      @fields = fields.map { |name, type| Field.new(name, type) }
+      @body = block
+    end
+  end
+end

spec/support/4_active_record_helper.rb

@@ -0,0 +1,45 @@
+# This file is responsible for one-time set up of ActiveRecord
+# 1 - Set ActiveRecord connection & options
+# 2 - Delete existing database
+# 3 - Expose "TestModels::ActiveRecord.initialize_model" to allow dynamically creating models
+require 'active_record'
+
+ActiveRecord::Base.logger = Logger.new($stdout)
+ActiveRecord::Base.logger.level = Logger::WARN
+ActiveRecord::Base.establish_connection(
+  'adapter' => defined?(JRUBY_VERSION) ? 'jdbcsqlite3' : 'sqlite3',
+  'database' => 'data.sqlite3',
+  'pool' => 5,
+  'timeout' => 5000
+)
+
+ActiveRecord::Base.raise_in_transactional_callbacks = true if ActiveRecord::Base.respond_to?(:raise_in_transactional_callbacks)
+
+FileUtils.rm_f('data.sqlite3')
+
+module Models
+  module ActiveRecord
+    def self.schema
+      @schema ||= ::ActiveRecord::Schema.new.tap { |schema| schema.verbose = false }
+    end
+
+    def self.initialize_model(specification)
+      schema.create_table specification.name.underscore.pluralize do |t|
+        specification.fields.each do |field|
+          t.send(field.type, field.name)
+        end
+      end
+
+      klass = Class.new(::ActiveRecord::Base) do
+        define_singleton_method(:model_name) do
+          name = "Models::ActiveRecord::#{specification.name}"
+          ActiveModel::Name.new(self, nil, name)
+        end
+      end
+
+      const_set(specification.name, klass)
+
+      klass.class_eval(&specification.body)
+    end
+  end
+end