Rails makes it super easy to write your tests. It starts by producing skeleton test code while you are creating your models and controllers.
By simply running your Rails tests you can ensure your code adheres to the desired functionality even after some major code refactoring.
Rails tests can also simulate browser requests and thus you can test your application's response without having to test it through your browser.
Introduction to Testing
-----------------------
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.
### The Test Environment
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 Sets up for Testing from the Word Go
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 `models` directory is meant to hold tests for your models, the `controllers` directory is meant to hold tests for your controllers and the `integration` directory is meant to hold tests that involve any number of controllers interacting.
_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
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. Keys which resemble YAML keywords such as 'yes' and 'no' are quoted so that the YAML Parser correctly interprets them.
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 Active Record. 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. We will be using examples from this generated code and will be supplementing it with additional examples where necessary.
A line by line examination of this file will help get you oriented to Rails testing code and terminology.
```ruby
require 'test_helper'
```
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 `ArticleTest` class defines a _test case_ because it inherits from `ActiveSupport::TestCase`. `ArticleTest` 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 class inherited from `Minitest::Test`
(which is the superclass of `ActiveSupport::TestCase`) that begins with `test_` (case sensitive) is simply called a test. So, `test_password` and `test_valid_password` are legal test names and are run automatically when the test case is run.
Rails adds a `test` method that takes a test name and a block. It generates a normal `Minitest::Unit` test with method names prefixed with `test_`. So,
only the `test` macro allows a more readable test name. You can still use regular method definitions though.
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.
```ruby
assert true
```
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:
* does this value = that value?
* is this object nil?
* does this line of code throw an exception?
* is the user's password greater than 5 characters?
Every test contains one or more assertions. Only when all the assertions are successful will the test pass.
In order to run your tests, your test database will need to have the current structure. The test helper checks whether your test database has any pending migrations. If so, it will try to load your `db/schema.rb` or `db/structure.sql` into the test database. If migrations are still pending, an error will be raised.
This will run all 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.
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:
```ruby
test "should report error" do
# some_undefined_variable is not defined elsewhere in the test case
some_undefined_variable
assert true
end
```
Now you can see even more output in the console from running the tests:
Notice the 'E' in the output. It denotes a test with 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.
| `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.
| `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. You can also pass an explicit status number or its symbolic equivalent. For more information, see [full list of status codes](http://rubydoc.info/github/rack/rack/master/Rack/Utils#HTTP_STATUS_CODES-constant) and how their [mapping](http://rubydoc.info/github/rack/rack/master/Rack/Utils#SYMBOL_TO_STATUS_CODE-constant) works.|
| `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. You can also pass named routes such as `assert_redirected_to root_path` and Active Record objects such as `assert_redirected_to @article`.|
| `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.
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.
### What to Include in your Functional Tests
You should test for things such as:
* was the web request successful?
* was the user redirected to the right page?
* was the user successfully authenticated?
* was the correct object stored in the response template?
* was the appropriate message displayed to the user in the view?
Now that we have used Rails scaffold generator for our `Article` resource, it has already created the controller code and tests. You can take look at the file `articles_controller_test.rb` in the `test/controllers` directory.
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 `articles` instance variable.
NOTE: If you try running `test_should_create_article` test from `articles_controller_test.rb` it will fail on account of the newly added model level validation and rightly so.
Now you can try running all the tests and they should pass.
### Available Request Types for Functional Tests
If you're familiar with the HTTP protocol, you'll know that `get` is a type of request. There are 6 request types supported in Rails functional tests:
*`get`
*`post`
*`patch`
*`put`
*`head`
*`delete`
All of request types are methods that you can use, however, you'll probably end up using the first two more often than the others.
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.
*`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.
### A Fuller Functional Test Example
Here's another example that uses `flash`, `assert_redirected_to`, and `assert_difference`:
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`.
There are two forms 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"
```
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
```
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.
```ruby
assert_select "ol" do |elements|
elements.each do |element|
assert_select element, "li", 4
end
end
assert_select "ol" do
assert_select "li", 8
end
```
The `assert_select` assertion is quite powerful. For more advanced usage, refer to its [documentation](http://api.rubyonrails.org/classes/ActionDispatch/Assertions/SelectorAssertions.html).
#### Additional View-Based Assertions
There are more assertions that are primarily used in testing views:
| `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.|
assert_select 'small', 'Please click the "Unsubscribe" link if you want to opt-out.'
end
```
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.
### Helpers Available for Integration Tests
In addition to the standard testing helpers, there are some additional helpers available to integration tests:
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
```ruby
require 'test_helper'
class UserFlowsTest <ActionDispatch::IntegrationTest
Ruby ships with a vast Standard Library for all common use-cases including testing. Since version 1.9, Ruby provides `Minitest`, a framework for testing. All the basic assertions such as `assert_equal` discussed above are actually defined in `Minitest::Assertions`. The classes `ActiveSupport::TestCase`, `ActionController::TestCase`, `ActionMailer::TestCase`, `ActionView::TestCase` and `ActionDispatch::IntegrationTest` - which we have been inheriting in our test classes - include `Minitest::Assertions`, allowing us to use all of the basic assertions in our tests.
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 `Articles` controller:
Above, the `setup` method is called before each test and so `@article` 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 `Articles` controller above should look like:
The goals of testing your mailer classes are to ensure that:
* emails are being processed (created and sent)
* the email content is correct (subject, sender, body, etc)
* the right emails are being sent at the right times
#### From All Sides
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.
### Unit Testing
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.
#### 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.
#### The Basic Test Case
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.
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:
```ruby
require 'test_helper'
class UserControllerTest <ActionController::TestCase
test "invite friend" do
assert_difference 'ActionMailer::Base.deliveries.size', +1 do
The built-in `minitest` 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: