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== Add a `to_squawk` method to String ==
To update a core class you will have to:
* Write tests for the desired functionality.
* Create a file for the code you wish to use.
* Require that file from your 'init.rb'.
Most plugins store their code classes in the plugin's lib directory. When you add a file to the lib directory, you must also require that file from 'init.rb'. The file you are going to add for this tutorial is 'lib/core_ext.rb'.
First, you need to write the tests. Testing plugins is very similar to testing rails apps. The generated test file should look something like this:
[source, ruby]
--------------------------------------------------------
# File: vendor/plugins/yaffle/test/core_ext_test.rb
require 'test/unit'
class CoreExtTest < Test::Unit::TestCase
# Replace this with your real tests.
def test_this_plugin
flunk
end
end
--------------------------------------------------------
Start off by removing the default test, and adding a require statement for your test helper.
[source, ruby]
--------------------------------------------------------
# File: vendor/plugins/yaffle/test/core_ext_test.rb
require 'test/unit'
require File.dirname(__FILE__) + '/test_helper.rb'
class CoreExtTest < Test::Unit::TestCase
end
--------------------------------------------------------
Navigate to your plugin directory and run `rake test`:
--------------------------------------------------------
cd vendor/plugins/yaffle
rake test
--------------------------------------------------------
Your test should fail with `no such file to load -- ./test/../lib/core_ext.rb (LoadError)` because we haven't created any file yet. Create the file 'lib/core_ext.rb' and re-run the tests. You should see a different error message:
--------------------------------------------------------
1.) Failure ...
No tests were specified
--------------------------------------------------------
Great - now you are ready to start development. The first thing we'll do is to add a method to String called `to_squawk` which will prefix the string with the word ``squawk!''. The test will look something like this:
[source, ruby]
--------------------------------------------------------
# File: vendor/plugins/yaffle/init.rb
class CoreExtTest < Test::Unit::TestCase
def test_string_should_respond_to_squawk
assert_equal true, "".respond_to?(:to_squawk)
end
def test_string_prepend_empty_strings_with_the_word_squawk
assert_equal "squawk!", "".to_squawk
end
def test_string_prepend_non_empty_strings_with_the_word_squawk
assert_equal "squawk! Hello World", "Hello World".to_squawk
end
end
--------------------------------------------------------
[source, ruby]
--------------------------------------------------------
# File: vendor/plugins/yaffle/init.rb
require "core_ext"
--------------------------------------------------------
[source, ruby]
--------------------------------------------------------
# File: vendor/plugins/yaffle/lib/core_ext.rb
String.class_eval do
def to_squawk
"squawk! #{self}".strip
end
end
--------------------------------------------------------
When monkey-patching existing classes it's often better to use `class_eval` instead of opening the class directly.
To test that your method does what it says it does, run the unit tests. To test this manually, fire up a console and start squawking:
--------------------------------------------------------
$ ./script/console
>> "Hello World".to_squawk
=> "squawk! Hello World"
--------------------------------------------------------
If that worked, congratulations! You just created your first test-driven plugin that extends a core ruby class.
|
