Add a logic error and detect it with a test

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Task

• Intentionally add a logic error to our app, so we can see another example of a test failure.

Steps

• Edit the app/controllers/limericks_controller.rb file to add a logic bug such that, in the index method, the call to Limerick.all.reverse_order is replaced with a call to Limerick.take(1) (which returns a collection of Limerick objects containing only 1 limerick).

class LimericksController < ApplicationController

  before_action :authenticate_user!, except: [:index]
  before_action :require_permission, except: [:index, :new, :create]

  def index
    @limericks = Limerick.take(1)
    render :index
  end

  ...

• Note that we have 2 Limerick test fixtures, but our app will now retrieve only 1 of them (due to the take(1) call).
  • In our LimericksControllerTest#should_get_index test case, the assertion assert_select 'div.card', limericks_size should now fail because the number of div.card elements printed will be 1, whereas the limericks_size value will be 2.
• Run all tests to check for errors.

rails test -v

• Inspect the output, which should look like this:

Running 1 tests in a single process (parallelization threshold is 50)
Run options: -v --seed 31239

# Running:

LimericksControllerTest#test_should_get_index = 2.24 s = F


Failure:
LimericksControllerTest#test_should_get_index [test/controllers/limericks_controller_test.rb:8]:
Expected exactly 2 elements matching "div.card", found 1..
Expected: 2
  Actual: 1


rails test test/controllers/limericks_controller_test.rb:4


Finished in 2.243783s, 0.4457 runs/s, 0.8914 assertions/s.
1 runs, 2 assertions, 1 failures, 0 errors, 0 skips

• Note that the assert_select 'div.card', limericks_size did indeed fail.
  • The test output reports a failure in the LimericksControllerTest#test_should_get_index test case on line 8 of the limericks_controller_test.rb file (where the assert_select call is found).
  • The output even mentions the cause of the assertion’s failure: “Expected exactly 2 elements matching "div.card", found 1..”.
  • This bug counts as a “failure” because it was caught by an assertion (and did not cause the system to crash as in the case of an “error”).
• Before moving on, correct the above bug and retest the code to ensure that the bug was fixed correctly.

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