Add a syntax error and detect it with a test

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Task

• Intentionally add a syntax error to our app, so we can see what test failures look like.

Steps

• Edit the app/controllers/limericks_controller.rb file to add a syntax error to the LimericksController#index method as follows.

class LimericksController < ApplicationController

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

  def index
    @limericks = Limerick.all.reverse_order
    renxxxxxxder :index
  end

  ...

• Note that the call to render is now an invalid call to a undefined method renxxxxxxder.
  • Although this example seems contrived, it is not uncommon for a developer to bump the keyboard while working in a file and to not notice the bug they introduced.
• 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 61993

# Running:

LimericksControllerTest#test_should_get_index = 0.15 s = E


Error:
LimericksControllerTest#test_should_get_index:
NoMethodError: undefined method `renxxxxxxder' for #<LimericksController:0x0000000000d1d8>

    renxxxxxxder :index
    ^^^^^^^^^^^^
    app/controllers/limericks_controller.rb:8:in `index'
    test/controllers/limericks_controller_test.rb:6:in `block in <class:LimericksControllerTest>'


rails test test/controllers/limericks_controller_test.rb:4


Finished in 0.153665s, 6.5077 runs/s, 0.0000 assertions/s.
1 runs, 0 assertions, 0 failures, 1 errors, 0 skips

• Note that error messages now appear in the test output.
  • We can see that the undefined method is mentioned (“NoMethodError: undefined method \renxxxxxxder'") and that the file and line number where the bug was made is also mentioned ("app/controllers/limericks_controller.rb:8:in `index’`”).
  • This bug is classified as an “error”, because it essentially made the system crash (unlike a “failure”, which is indicative of a failed assert call).
• Before moving on, correct the above bug and retest the code to ensure that the bug was fixed correctly.

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