Testing a Rails engine that depends on its hosting application can be done using integration tests. An integration test allows you to test the interactions between the engine and the hosting application to ensure that they work together as expected. Here's a step-by-step guide on how to do it:

  1. Set up your Rails Engine Testing Environment:

    • Create a new Rails application to serve as the hosting application for the engine if you don't have one already.
    • Add your engine gem to the Gemfile of the hosting application. You can do this by using a local path or specifying the GitHub repository.
    • Run bundle install to install the engine gem and its dependencies.
  2. Configure the Rails Engine Routes in the Hosting Application:

    • Mount your engine's routes in the config/routes.rb file of the hosting application. This makes the engine's routes accessible within the hosting application's test environment.
# config/routes.rb Rails.application.routes.draw do # ... mount YourEngine::Engine => '/your_engine', as: 'your_engine_prefix' # ... end
  1. Generate Engine Test Skeleton:

    • Run the following command to generate the necessary test files for your engine:
      rails generate your_engine:install
  2. Write Integration Tests:

    • In the generated test directory of your hosting application, you'll find the folder dummy that contains a sample integration test file. You can use this file as a reference for writing your integration tests.

    • Create new integration test files in the test directory or any subdirectory within it. Name your test files with a _test.rb extension.

    • Inside your integration test files, you can now write tests that interact with both the engine and the hosting application. Use methods like get, post, patch, delete, etc., to simulate HTTP requests to the engine's routes.

# test/integration/my_engine_integration_test.rb require 'test_helper' class MyEngineIntegrationTest < ActionDispatch::IntegrationTest test 'should get index from engine' do get your_engine_prefix.root_path assert_response :success end test 'should get show from engine' do get your_engine_prefix.some_resource_path(some_resource_id) assert_response :success end # Write more integration tests as needed end
  1. Run the Tests:

    • Execute the integration tests with the following command:
      rails test

    This command will run both your hosting application's tests and the engine's integration tests.

  2. Test Environment Configuration:

    • Make sure your test environment is properly set up to load the engine. Ensure that the engine's migrations, routes, and configurations are properly loaded during the test runs.

With the integration tests in place, you can now verify that your Rails engine interacts correctly with its hosting application. It's essential to include tests that cover various scenarios to ensure the robustness and reliability of your engine in different usage scenarios.

Keep in mind that the above steps may vary slightly depending on the specific setup and configuration of your Rails engine and hosting application. Always refer to the official documentation and guides of your engine and Rails version for the most accurate and up-to-date information.

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