How to Test Controller in Rails: Simple Guide with Examples

To test a controller in Rails, use ActionDispatch::IntegrationTest or ActionController::TestCase with methods like get, post, patch, and delete to simulate requests. Then, assert the response status, rendered templates, or assigned variables to verify controller behavior.

Syntax

Rails controller tests simulate HTTP requests to controller actions and check responses. Use methods like get :action_name to call an action. Then use assertions like assert_response :success to check the HTTP status or assert_template to verify the rendered view.

In modern Rails, integration tests with get url are preferred for full request cycles.

ruby

class ArticlesControllerTest < ActionDispatch::IntegrationTest
  test "should get index" do
    get articles_url
    assert_response :success
    assert_select 'h1', 'Articles'
  end
end

Example

This example shows a simple test for the index action of an Articles controller. It sends a GET request to the index URL, checks for a successful response, and verifies that the page contains an h1 heading with the text 'Articles'.

ruby

require 'test_helper'

class ArticlesControllerTest < ActionDispatch::IntegrationTest
  test "should get index" do
    get articles_url
    assert_response :success
    assert_select 'h1', 'Articles'
  end

  test "should create article" do
    assert_difference('Article.count') do
      post articles_url, params: { article: { title: 'New Article', body: 'Content here' } }
    end
    assert_redirected_to article_url(Article.last)
  end
end

Output

Run options: --seed 12345

# Running:

..

Finished in 0.12345s, 16.19 runs/s, 32.38 assertions/s.

2 runs, 4 assertions, 0 failures, 0 errors, 0 skips

Common Pitfalls

• Using ActionController::TestCase instead of ActionDispatch::IntegrationTest in new Rails versions can limit test coverage.
• Not passing params: hash correctly when testing post or patch requests causes errors.
• Forgetting to assert the response or redirect leads to tests that pass without verifying behavior.
• Testing controller internals like instance variables instead of response or behavior is discouraged.

ruby

class WrongControllerTest < ActionController::TestCase
  test "wrong post without params" do
    post :create
    assert_response :redirect
  end
end

# Correct way:
class RightControllerTest < ActionDispatch::IntegrationTest
  test "correct post with params" do
    post articles_url, params: { article: { title: 'Test', body: 'Body' } }
    assert_redirected_to article_url(Article.last)
  end
end

Quick Reference

Here is a quick summary of common test methods and assertions for Rails controller tests:

Method / Assertion	Purpose
get :action or get url	Simulate GET request to controller action or URL
post :action or post url, params:	Simulate POST request with parameters
patch :action or patch url, params:	Simulate PATCH request with parameters
delete :action or delete url	Simulate DELETE request
assert_response :success	Check HTTP 200 OK response
assert_redirected_to url	Check redirection to a URL
assert_select 'selector', 'text'	Check HTML content in response
assert_difference('Model.count')	Check that a record count changes

Key Takeaways

Use ActionDispatch::IntegrationTest with HTTP methods to test controller actions fully.

Always pass params as a hash when testing POST, PATCH, or DELETE requests.

Assert response status and content to verify controller behavior.

Avoid testing controller internals; focus on request and response.

Use assert_select to check rendered HTML elements in the response.