Controller tests in Ruby on Rails - Step-by-Step Execution

Concept Flow - Controller tests

Write test for controller action

↓

Run test suite

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Rails runs controller action

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Controller processes request

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Controller returns response

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Test checks response and side effects

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Test passes or fails

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Fix code or test if needed

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Repeat

Controller tests run your Rails controller actions and check their responses and effects step-by-step.

Execution Sample

Ruby on Rails

test "should get index" do
  get :index
  assert_response :success
  assert_not_nil assigns(:items)
end

This test calls the index action, checks for success response, and verifies assigned variables.

Execution Table

Step	Action	Controller State	Response	Test Assertion	Result
1	Call get :index	Processing index action	Pending	None yet	Continue
2	Controller fetches items	Items loaded into @items	Pending	None yet	Continue
3	Controller renders index view	Ready to respond	200 OK	assert_response :success	Pass
4	Test checks assigns(:items)	@items present	200 OK	assert_not_nil assigns(:items)	Pass
5	Test ends	Completed	200 OK	All assertions passed	Test Passed

💡 Test ends after all assertions pass or fail

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
@items	nil	Array of items loaded	Array of items loaded	Array of items loaded

Key Moments - 3 Insights

Why does the test check 'assigns(:items)' after calling get :index?

Because the controller sets @items in the index action, the test verifies it to ensure the controller prepared data for the view (see execution_table step 4).

What does 'assert_response :success' check in the test?

It checks that the controller responded with HTTP status 200 OK, meaning the request was handled successfully (see execution_table step 3).

Why do we call 'get :index' in the test?

Calling 'get :index' simulates a browser requesting the index page, triggering the controller action to run (see execution_table step 1).

Visual Quiz - 3 Questions

Look at the execution table, what is the response status after the controller renders the index view?

A 200 OK

B 404 Not Found

C 500 Internal Server Error

D 302 Redirect

💡 Hint

Check the Response column at Step 3 in the execution_table

At which step does the test verify that @items is not nil?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the Test Assertion column in the execution_table

If the controller did not assign @items, which test assertion would fail?

A assert_response :success

B get :index

C assert_not_nil assigns(:items)

D Test ends

💡 Hint

Refer to the assertion checking assigns(:items) in execution_table step 4

Concept Snapshot

Controller tests in Rails:
- Use HTTP verbs like get, post to call actions
- Check response status with assert_response
- Verify instance variables with assigns(:var)
- Ensure controller processes requests and renders views correctly
- Run tests to catch errors early

Full Transcript

Controller tests in Rails simulate browser requests to controller actions. The test calls an action like index using get :index. The controller runs the action, loads data into instance variables like @items, and renders a view. The test then checks the HTTP response status to confirm success and verifies that expected variables are assigned. If all assertions pass, the test passes. This process helps ensure your controller behaves as expected before deploying your app.