Add support for using an ARCONFIG environment variable to specify the location of the config.yml file for running the tests

activerecord/RUNNING_UNIT_TESTS

@@ -32,3 +32,8 @@ By default the tests run with the Identity Map turned off. But all tests should
 not the identity map is on or off. You can turn it on using the IM env variable:
 
   $ IM=true ruby -Itest test/case/base_test.rb
+
+== Config file
+
+By default, the config file is expected to be at the path test/config.yml. You can specify a
+custom location with the ARCONFIG environment variable.

activerecord/test/support/config.rb

@@ -10,13 +10,16 @@ module ARTest
 
     private
 
+    def config_file
+      Pathname.new(ENV['ARCONFIG'] || TEST_ROOT + '/config.yml')
+    end
+
     def read_config
-      unless File.exist?(TEST_ROOT + '/config.yml')
-        FileUtils.cp TEST_ROOT + '/config.example.yml', TEST_ROOT + '/config.yml'
+      unless config_file.exist?
+        FileUtils.cp TEST_ROOT + '/config.example.yml', config_file
       end
 
-      raw = File.read(TEST_ROOT + '/config.yml')
-      erb = Erubis::Eruby.new(raw)
+      erb = Erubis::Eruby.new(config_file.read)
       expand_config(YAML.parse(erb.result(binding)).transform)
     end