Testing support was woven into the Rails fabric from the beginning. It wasn't an "oh! let's bolt on support for running tests because they're new and cool" epiphany. Just about every Rails application interacts heavily with a database and, as a result, your tests will need a database to interact with as well. To write efficient tests, you'll need to understand how to set up this database and populate it with sample data.
By default, every Rails application has three environments: development, test, and production. The database for each one of them is configured in +config/database.yml+.
A dedicated test database allows you to set up and interact with test data in isolation. Tests can mangle test data with confidence, that won't touch the data in the development or production databases.
Rails creates a +test+ folder for you as soon as you create a Rails project using +rails new+ _application_name_. If you list the contents of this folder then you shall see:
The +unit+ directory is meant to hold tests for your models, the +functional+ directory is meant to hold tests for your controllers, the +integration+ directory is meant to hold tests that involve any number of controllers interacting, and the +performance+ directory is meant for performance tests.
Fixtures are a way of organizing test data; they reside in the +fixtures+ folder.
The +test_helper.rb+ file holds the default configuration for your tests.
_Fixtures_ is a fancy word for sample data. Fixtures allow you to populate your testing database with predefined data before your tests run. Fixtures are database independent written in YAML. There is one file per model.
You'll find fixtures under your +test/fixtures+ directory. When you run +rails generate model+ to create a new model fixture stubs will be automatically created and placed in this directory.
YAML-formatted fixtures are a very human-friendly way to describe your sample data. These types of fixtures have the *.yml* file extension (as in +users.yml+).
Each fixture is given a name followed by an indented list of colon-separated key/value pairs. Records are typically separated by a blank space. You can place comments in a fixture file by using the # character in the first column.
ERB allows you to embed Ruby code within templates. The YAML fixture format is pre-processed with ERB when Rails loads fixtures. This allows you to use Ruby to help you generate some sample data. For example, the following code generates a thousand users:
Fixtures are instances of ActiveRecord. As mentioned in point #3 above, you can access the object directly because it is automatically setup as a local variable of the test case. For example:
For this guide we will be using Rails _scaffolding_. It will create the model, a migration, controller and views for the new resource in a single operation. It will also create a full test suite following Rails best practices. I will be using examples from this generated code and will be supplementing it with additional examples where necessary.
As you know by now, +test_helper.rb+ specifies the default configuration to run our tests. This is included with all the tests, so any methods added to this file are available to all your tests.
The +PostTest+ class defines a _test case_ because it inherits from +ActiveSupport::TestCase+. +PostTest+ thus has all the methods available from +ActiveSupport::TestCase+. You'll see those methods a little later in this guide.
Any method defined within a +Test::Unit+ test case that begins with +test+ (case sensitive) is simply called a test. So, +test_password+, +test_valid_password+ and +testValidPassword+ all are legal test names and are run automatically when the test case is run.
NOTE: The method name is generated by replacing spaces with underscores. The result does not need to be a valid Ruby identifier though, the name may contain punctuation characters etc. That's because in Ruby technically any string may be a method name. Odd ones need +define_method+ and +send+ calls, but formally there's no restriction.
This line of code is called an _assertion_. An assertion is a line of code that evaluates an object (or expression) for expected results. For example, an assertion can check:
The +rake db:migrate+ above runs any pending migrations on the _development_ environment and updates +db/schema.rb+. The +rake db:test:load+ recreates the test database from the current +db/schema.rb+. On subsequent attempts, it is a good idea to first run +db:test:prepare+, as it first checks for pending migrations and warns you appropriately.
This will run all the test methods from the test case. Note that +test_helper.rb+ is in the +test+ directory, hence this directory needs to be added to the load path using the +-I+ switch.
The +.+ (dot) above indicates a passing test. When a test fails you see an +F+; when a test throws an error you see an +E+ in its place. The last line of the output is the summary.
To see how a test failure is reported, you can add a failing test to the +post_test.rb+ test case.
In the output, +F+ denotes a failure. You can see the corresponding trace shown under +1)+ along with the name of the failing test. The next few lines contain the stack trace followed by a message which mentions the actual value and the expected value by the assertion. The default assertion messages provide just enough information to help pinpoint the error. To make the assertion failure message more readable, every assertion provides an optional message parameter, as shown here:
Now, if you noticed, we first wrote a test which fails for a desired functionality, then we wrote some code which adds the functionality and finally we ensured that our test passes. This approach to software development is referred to as _Test-Driven Development_ (TDD).
TIP: Many Rails developers practice _Test-Driven Development_ (TDD). This is an excellent way to build up a test suite that exercises every part of your application. TDD is beyond the scope of this guide, but one place to start is with "15 TDD steps to create a Rails application":http://andrzejonsoftware.blogspot.com/2007/05/15-tdd-steps-to-create-rails.html.
To see how an error gets reported, here's a test containing an error:
NOTE: The execution of each test method stops as soon as any error or an assertion failure is encountered, and the test suite continues with the next method. All test methods are executed in alphabetical order.
Ideally, you would like to include a test for everything which could possibly break. It's a good practice to have at least one test for each of your validations and at least one test for every method in your model.
By now you've caught a glimpse of some of the assertions that are available. Assertions are the worker bees of testing. They are the ones that actually perform the checks to ensure that things are going as planned.
There are a bunch of different types of assertions you can use. Here's the complete list of assertions that ship with +test/unit+, the default testing library used by Rails. The +[msg]+ parameter is an optional string message you can specify to make your test failure messages clearer. It's not required.
|+assert_nothing_raised( exception1, exception2, ... ) { block }+ |Ensures that the given block doesn't raise one of the given exceptions.|
|+assert_instance_of( class, obj, [msg] )+ |Ensures that +obj+ is of the +class+ type.|
|+assert_kind_of( class, obj, [msg] )+ |Ensures that +obj+ is or descends from +class+.|
|+assert_respond_to( obj, symbol, [msg] )+ |Ensures that +obj+ has a method called +symbol+.|
|+assert_operator( obj1, operator, obj2, [msg] )+ |Ensures that +obj1.operator(obj2)+ is true.|
|+assert_send( array, [msg] )+ |Ensures that executing the method listed in +array[1]+ on the object in +array[0]+ with the parameters of +array[2 and up]+ is true. This one is weird eh?|
|+flunk( [msg] )+ |Ensures failure. This is useful to explicitly mark a test that isn't finished yet.|
Because of the modular nature of the testing framework, it is possible to create your own assertions. In fact, that's exactly what Rails does. It includes some specialized assertions to make your life easier.
NOTE: Creating your own assertions is an advanced topic that we won't cover in this tutorial.
h4. Rails Specific Assertions
Rails adds some custom assertions of its own to the +test/unit+ framework:
|+assert_difference(expressions, difference = 1, message = nil) {...}+ |Test numeric difference between the return value of an expression as a result of what is evaluated in the yielded block.|
|+assert_no_difference(expressions, message = nil, &block)+ |Asserts that the numeric result of evaluating an expression is not changed before and after invoking the passed in block.|
|+assert_recognizes(expected_options, path, extras={}, message=nil)+ |Asserts that the routing of the given path was handled correctly and that the parsed options (given in the expected_options hash) match path. Basically, it asserts that Rails recognizes the route given by expected_options.|
|+assert_generates(expected_path, options, defaults={}, extras = {}, message=nil)+ |Asserts that the provided options can be used to generate the provided path. This is the inverse of assert_recognizes. The extras parameter is used to tell the request the names and values of additional request parameters that would be in a query string. The message parameter allows you to specify a custom error message for assertion failures.|
|+assert_response(type, message = nil)+ |Asserts that the response comes with a specific status code. You can specify +:success+ to indicate 200-299, +:redirect+ to indicate 300-399, +:missing+ to indicate 404, or +:error+ to match the 500-599 range|
|+assert_redirected_to(options = {}, message=nil)+ |Assert that the redirection options passed in match those of the redirect called in the latest action. This match can be partial, such that +assert_redirected_to(:controller => "weblog")+ will also match the redirection of +redirect_to(:controller => "weblog", :action => "show")+ and so on.|
|+assert_template(expected = nil, message=nil)+ |Asserts that the request was rendered with the appropriate template file.|
You'll see the usage of some of these assertions in the next chapter.
h3. Functional Tests for Your Controllers
In Rails, testing the various actions of a single controller is called writing functional tests for that controller. Controllers handle the incoming web requests to your application and eventually respond with a rendered view.
Now that we have used Rails scaffold generator for our +Post+ resource, it has already created the controller code and functional tests. You can take look at the file +posts_controller_test.rb+ in the +test/functional+ directory.
Let me take you through one such test, +test_should_get_index+ from the file +posts_controller_test.rb+.
In the +test_should_get_index+ test, Rails simulates a request on the action called +index+, making sure the request was successful and also ensuring that it assigns a valid +posts+ instance variable.
NOTE: If you try running +test_should_create_post+ test from +posts_controller_test.rb+ it will fail on account of the newly added model level validation and rightly so.
Let us modify +test_should_create_post+ test in +posts_controller_test.rb+ so that all our test pass:
NOTE: Functional tests do not verify whether the specified request type should be accepted by the action. Request types in this context exist to make your tests more descriptive.
After a request has been made by using one of the 5 methods (+get+, +post+, etc.) and processed, you will have 4 Hash objects ready for use:
* +assigns+ - Any objects that are stored as instance variables in actions for use in views.
* +cookies+ - Any cookies that are set.
* +flash+ - Any objects living in the flash.
* +session+ - Any object living in session variables.
As is the case with normal Hash objects, you can access the values by referencing the keys by string. You can also reference them by symbol name, except for +assigns+. For example:
is the correct way to assert for the layout when the view renders a partial with name +_form+. Omitting the +:partial+ key in your +assert_template+ call will complain.
post :create, :post => { :title => 'Hi', :body => 'This is my first post.'}
end
assert_redirected_to post_path(assigns(:post))
assert_equal 'Post was successfully created.', flash[:notice]
end
</ruby>
h4. Testing Views
Testing the response to your request by asserting the presence of key HTML elements and their content is a useful way to test the views of your application. The +assert_select+ assertion allows you to do this by using a simple yet powerful syntax.
NOTE: You may find references to +assert_tag+ in other documentation, but this is now deprecated in favor of +assert_select+.
+assert_select(selector, [equality], [message])+ ensures that the equality condition is met on the selected elements through the selector. The selector may be a CSS selector expression (String), an expression with substitution values, or an +HTML::Selector+ object.
+assert_select(element, selector, [equality], [message])+ ensures that the equality condition is met on all the selected elements through the selector starting from the _element_ (instance of +HTML::Node+) and its descendants.
For example, you could verify the contents on the title element in your response with:
<ruby>
assert_select 'title', "Welcome to Rails Testing Guide"
</ruby>
You can also use nested +assert_select+ blocks. In this case the inner +assert_select+ runs the assertion on the complete collection of elements selected by the outer +assert_select+ block:
<ruby>
assert_select 'ul.navigation' do
assert_select 'li.menu_item'
end
</ruby>
Alternatively the collection of elements selected by the outer +assert_select+ may be iterated through so that +assert_select+ may be called separately for each element. Suppose for example that the response contains two ordered lists, each with four list elements then the following tests will both pass.
The +assert_select+ assertion is quite powerful. For more advanced usage, refer to its "documentation":http://api.rubyonrails.org/classes/ActionDispatch/Assertions/SelectorAssertions.html.
|+assert_select_email+ |Allows you to make assertions on the body of an e-mail. |
|+assert_select_encoded+ |Allows you to make assertions on encoded HTML. It does this by un-encoding the contents of each element and then calling the block with all the un-encoded elements.|
|+css_select(selector)+ or +css_select(element, selector)+ |Returns an array of all the elements selected by the _selector_. In the second variant it first matches the base _element_ and tries to match the _selector_ expression on any of its children. If there are no matches both variants return an empty array.|
Here's an example of using +assert_select_email+:
<ruby>
assert_select_email do
assert_select 'small', 'Please click the "Unsubscribe" link if you want to opt-out.'
end
</ruby>
h3. Integration Testing
Integration tests are used to test the interaction among any number of controllers. They are generally used to test important work flows within your application.
Unlike Unit and Functional tests, integration tests have to be explicitly created under the 'test/integration' folder within your application. Rails provides a generator to create an integration test skeleton for you.
Integration tests inherit from +ActionDispatch::IntegrationTest+. This makes available some additional helpers to use in your integration tests. Also you need to explicitly include the fixtures to be made available to the test.
As you can see the integration test involves multiple controllers and exercises the entire stack from database to dispatcher. In addition you can have multiple session instances open simultaneously in a test and extend those instances with assertion methods to create a very powerful testing DSL (domain-specific language) just for your application.
Here's an example of multiple sessions and custom DSL in an integration test
You don't need to set up and run your tests by hand on a test-by-test basis. Rails comes with a number of rake tasks to help in testing. The table below lists all rake tasks that come along in the default Rakefile when you initiate a Rails project.
Ruby ships with a boat load of libraries. One little gem of a library is +Test::Unit+, a framework for unit testing in Ruby. All the basic assertions discussed above are actually defined in +Test::Unit::Assertions+. The class +ActiveSupport::TestCase+ which we have been using in our unit and functional tests extends +Test::Unit::TestCase+, allowing
us to use all of the basic assertions in our tests.
NOTE: For more information on +Test::Unit+, refer to "test/unit Documentation":http://ruby-doc.org/stdlib/libdoc/test/unit/rdoc/
h3. Setup and Teardown
If you would like to run a block of code before the start of each test and another block of code after the end of each test you have two special callbacks for your rescue. Let's take note of this by looking at an example for our functional test in +Posts+ controller:
<ruby>
require 'test_helper'
class PostsControllerTest <ActionController::TestCase
# called before every single test
def setup
@post = posts(:one)
end
# called after every single test
def teardown
# as we are re-initializing @post before every test
# setting it to nil here is not essential but I hope
# you understand how you can use the teardown method
Above, the +setup+ method is called before each test and so +@post+ is available for each of the tests. Rails implements +setup+ and +teardown+ as +ActiveSupport::Callbacks+. Which essentially means you need not only use +setup+ and +teardown+ as methods in your tests. You could specify them by using:
Like everything else in your Rails application, it is recommended that you test your routes. An example test for a route in the default +show+ action of +Posts+ controller above should look like:
There are two aspects of testing your mailer, the unit tests and the functional tests. In the unit tests, you run the mailer in isolation with tightly controlled inputs and compare the output to a known value (a fixture.) In the functional tests you don't so much test the minute details produced by the mailer; instead, we test that our controllers and models are using the mailer in the right way. You test to prove that the right email was sent at the right time.
In order to test that your mailer is working as expected, you can use unit tests to compare the actual results of the mailer with pre-written examples of what should be produced.
h5. Revenge of the Fixtures
For the purposes of unit testing a mailer, fixtures are used to provide an example of how the output _should_ look. Because these are example emails, and not Active Record data like the other fixtures, they are kept in their own subdirectory apart from the other fixtures. The name of the directory within +test/fixtures+ directly corresponds to the name of the mailer. So, for a mailer named +UserMailer+, the fixtures should reside in +test/fixtures/user_mailer+ directory.
When you generated your mailer, the generator creates stub fixtures for each of the mailers actions. If you didn't use the generator you'll have to make those files yourself.
Here's a unit test to test a mailer named +UserMailer+ whose action +invite+ is used to send an invitation to a friend. It is an adapted version of the base test created by the generator for an +invite+ action.
In this test, +@expected+ is an instance of +TMail::Mail+ that you can use in your tests. It is defined in +ActionMailer::TestCase+. The test above uses +@expected+ to construct an email, which it then asserts with email created by the custom mailer. The +invite+ fixture is the body of the email and is used as the sample content to assert against. The helper +read_fixture+ is used to read in the content from this file.
Here's the content of the +invite+ fixture:
<pre>
Hi friend@example.com,
You have been invited.
Cheers!
</pre>
This is the right time to understand a little more about writing tests for your mailers. The line +ActionMailer::Base.delivery_method = :test+ in +config/environments/test.rb+ sets the delivery method to test mode so that email will not actually be delivered (useful to avoid spamming your users while testing) but instead it will be appended to an array (+ActionMailer::Base.deliveries+).
However often in unit tests, mails will not actually be sent, simply constructed, as in the example above, where the precise content of the email is checked against what it should be.
Functional testing for mailers involves more than just checking that the email body, recipients and so forth are correct. In functional mail tests you call the mail deliver methods and check that the appropriate emails have been appended to the delivery list. It is fairly safe to assume that the deliver methods themselves do their job. You are probably more interested in whether your own business logic is sending emails when you expect them to go out. For example, you can check that the invite friend operation is sending an email appropriately:
The built-in +test/unit+ based testing is not the only way to test Rails applications. Rails developers have come up with a wide variety of other approaches and aids for testing, including:
* "NullDB":http://avdi.org/projects/nulldb/, a way to speed up testing by avoiding database use.
