`assert_template` always succeeds when passed locals in an ActionController::TestCase

[opsidao]

As can be seen in the code, when you mistakenly pass the locals parameter to assert_template the assertion will simply write a message to the terminal, not even labeled as a warning in any way, but the assertion will the proceed to succeed regardless of what you pass to it.

A small test case follows:

# config/routes.rb
Rails.application.routes.draw do
  get 'failling' => 'failling#index'
end

# app/controllers/failling_controller.rb
class FaillingController < ActionController::Base
  def index
    head :ok
  end
end

# test/controllers/failling_controller_test.rb
require 'test_helper'

class FaillingControllerTest < ActionController::TestCase
  tests FaillingController

  test 'unexpected success' do
    get :index

    assert_response 200
    assert_template partial: 'totally made up partial',
                    locals: { if_this_is_here: "then it doesn't matter" }
  end
end

Executing this test I would expect a failure, but it succeeds just writing the message to the console:

Started with run options --seed 41249


# Running tests with run options --seed 41249:

FaillingControllerTest
the :locals option to #assert_template is only supported in a ActionView::TestCase
  test_unexpected_success                                         PASS (0.08s)
.
Finished in 0.08816s
1 tests, 1 assertions, 0 failures, 0 errors, 0 skips


Finished tests in 0.088958s, 11.2413 tests/s, 11.2413 assertions/s.


1 tests, 1 assertions, 0 failures, 0 errors, 0 skips

I think that in this case, the correct behaviour would be for the assertion to fail.