Testing a patch to the Rails mysql adapter - ruby-on-rails

Question

I wrote a little monkeypatch to the Rails MySQLAdapter and want to package it up to use it in my other projects. I am trying to write some tests for it but I am still new to testing and I am not sure how to test this. Can someone help get me started?
Here is the code I want to test:
unless RAILS_ENV == 'production'
module ActiveRecord
module ConnectionAdapters
class MysqlAdapter < AbstractAdapter
def select_with_explain(sql, name = nil)
explanation = execute_with_disable_logging('EXPLAIN ' + sql)
e = explanation.all_hashes.first
exp = e.collect{|k,v| " | #{k}: #{v} "}.join
log(exp, 'Explain')
select_without_explain(sql, name)
end
def execute_with_disable_logging(sql, name = nil) #:nodoc:
#Run a query without logging
#connection.query(sql)
rescue ActiveRecord::StatementInvalid => exception
if exception.message.split(":").first =~ /Packets out of order/
raise ActiveRecord::StatementInvalid, "'Packets out of order' error was received from the database. Please update your mysql bindings (gem install mysql) and read http://dev.mysql.com/doc/mysql/en/password-hashing.html for more information. If you're on Windows, use the Instant Rails installer to get the updated mysql bindings."
else
raise
end
end
alias_method_chain :select, :explain
end
end
end
end
Thanks.

Answer 1

General testing
You could start reading about testing.
After you are understanding the basics of testing, you should think what you have changed. Then make some tests which test for
the original situation, resulting in errors since you updated it. So reverse the test after it indeed is working for the original situation.
the new situation to see whether you have implemented your idea correctly
The hardest part is to be sure that you covered all situations. Finally, if both parts pass then you could say that your code it working as expected.
Testing gems
In order to test gems you can run
rake test:plugins
to test all plugins of your rails application (see more in chapter 6 of the testing guide), this only works when the gem is in the vendor directory of an application.
Another possibility is to modify the Rakefile of the gem by including a testing task. For example this
desc 'Test my custom made gem.'
Rake::TestTask.new(:test) do |t|
t.libs << 'lib'
t.libs << 'test'
t.pattern = 'test/**/*_test.rb'
t.verbose = true
end
would run all available tests in the test directory ending with _test.rb. To execute this test you can type rake test (from the gem directory!).
In order to run the tests for the gem by default (when typing just rake) you can add/modify this line:
task :default => :test
I used the second method in my ruby-bbcode gem, so you could take a look at it to see the complete example.