Testing Controllers

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Testing Rails Applications - Integration Testing(DOCUMENTATION)

Introduction

Controller tests (integration tests in modern Rails) verify that your application handles HTTP requests correctly, returns proper status codes, and renders the right templates.

Key Concepts

  • Integration test: A test that simulates HTTP requests (GET, POST, PATCH, DELETE) against your application.
  • assert_response: Verifies the HTTP status code of the response (:success, :redirect, :not_found).
  • assert_redirected_to: Verifies that the response redirected to a specific URL.
  • assert_difference: Commonly used to verify that POST/DELETE actions change record counts.

Real World Context

Controller tests verify the full request cycle: routing, authentication, parameter handling, and response. They catch issues like broken routes, missing authentication checks, and incorrect redirects that model tests cannot detect.

Deep Dive

Basic Controller Tests

ruby
class ArticlesControllerTest < ActionDispatch::IntegrationTest
  setup do
    @article = articles(:published_article)
  end

  test "should get index" do
    get articles_url
    assert_response :success
  end

  test "should get show" do
    get article_url(@article)
    assert_response :success
  end
end

Testing CRUD Operations

ruby
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

test "should update article" do
  patch article_url(@article), params: {
    article: { title: "Updated Title" }
  }
  assert_redirected_to article_url(@article)
  @article.reload
  assert_equal "Updated Title", @article.title
end

test "should destroy article" do
  assert_difference("Article.count", -1) do
    delete article_url(@article)
  end
  assert_redirected_to articles_url
end

Testing Invalid Data

ruby
test "should not create article with invalid data" do
  assert_no_difference("Article.count") do
    post articles_url, params: {
      article: { title: "", body: "" }
    }
  end
  assert_response :unprocessable_entity
end

Testing with Authentication

ruby
test "should redirect create when not logged in" do
  post articles_url, params: { article: { title: "Test" } }
  assert_redirected_to login_url
end

test "should create article when logged in" do
  post login_url, params: { email: @user.email, password: "password" }
  assert_difference("Article.count") do
    post articles_url, params: { article: { title: "New", body: "Content" } }
  end
end

Testing JSON APIs

ruby
test "should return articles as JSON" do
  get articles_url, as: :json
  assert_response :success
  json = JSON.parse(response.body)
  assert_kind_of Array, json
end

Common Pitfalls

  • Forgetting .reload: After a PATCH request, the local variable still holds old data. Call @article.reload before asserting updated values.
  • Not testing unauthorized access: Always test that protected actions redirect unauthenticated users.
  • Skipping negative tests: Test that invalid data returns :unprocessable_entity and does not create records.

Best Practices

  • Test both authenticated and unauthenticated access for protected actions.
  • Use assert_difference and assert_no_difference to verify data changes.
  • Always check both the response status and any side effects (redirects, database changes).

Summary

  • Controller tests use get, post, patch, delete to simulate HTTP requests.
  • assert_response :success checks for 200-range status codes.
  • assert_redirected_to verifies redirect destinations.
  • assert_difference confirms that create/destroy operations modify the database.
  • Test both valid and invalid inputs, and both authenticated and unauthenticated access.

Code Examples

ruby
class ArticlesControllerTest < ActionDispatch::IntegrationTest
  test "should get index" do
    get articles_url
    assert_response :success
  end

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