Why Doesn't Minitest::Spec Have a Wont_Raise Assertion

Why doesn't MiniTest::Spec have a wont_raise assertion?

MiniTest does implement assert_nothing_raised in its Test::Unit compatibility layer, but in its own tests (MiniTest::Unit and MiniTest::Spec) it does not implement any test like this. The reason is, the programmer argues, that testing for nothing raised is not a test of anything; you never expect anything to be raised in a test, except when you are testing for an exception. If an unexpected (uncaught) exception occurs in the code for a test, you'll get an exception reported in good order by the test and you'll know you have a problem.

Example:

require 'minitest/autorun'

describe "something" do
  it "does something" do
    Ooops
  end
end

Output:

Run options: --seed 41521

# Running tests:

E

Finished tests in 0.000729s, 1371.7421 tests/s, 0.0000 assertions/s.

  1) Error:
test_0001_does_something(something):
NameError: uninitialized constant Ooops
    untitled:5:in `block (2 levels) in <main>'

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

Which is exactly what you wanted to know. If you were expecting nothing to be raised, you didn't get it and you've been told so.

So, the argument here is: do not use assert_nothing_raised! It's just a meaningless crutch. See, for example:

https://github.com/seattlerb/minitest/issues/70

https://github.com/seattlerb/minitest/issues/159

http://blog.zenspider.com/blog/2012/01/assert_nothing_tested.html

On the other hand, clearly assert_nothing_raised corresponds to some intuition among users, since so many people expect a wont_raise to go with must_raise, etc. In particular one would like to focus an assertion on this, not merely a test. Luckily, MiniTest is extremely minimalist and flexible, so if you want to add your own routine, you can. So you can write a method that tests for no exception and returns a known outcome if there is no exception, and now you can assert for that known outcome.

For example (I'm not saying this is perfect, just showing the idea):

class TestMyRequire < MiniTest::Spec
  def testForError # pass me a block and I'll tell you if it raised
    yield
    "ok"
  rescue
    $!
  end
  it "blends" do
    testForError do
      something_or_other
    end.must_equal "ok"
  end
end

The point is not that this is a good or bad idea but that it was never the responsibility of MiniTest to do it for you.

Why doesn't Minitest's assert_raises work as expected in this case?

This isn't a problem with assert_raises, that continues to work just fine. The issue you are having is that the exception you are raising within your Rails app is getting handled by your Rails app and not propagating out to your test. Calling get '/missing' is raising the AbstractController::ActionNotFound error, but then your app handles the error and returns an appropriate response (404 or 500) to the client (your test).

Okay, so how would you go about testing that your controller really did raise the error you are expecting? Normally you would just use an ActionController::TestCase test to test your controllers. But, when you call an action on a controller that doesn't in ActionController::TestCase you get a different error. So the following:

require "test_helper"

class TestControllerTest < ActionController::TestCase

  def test_missing
    assert_raises AbstractController::ActionNotFound do
      get :missing
    end
  end
end

Produces the following output:

  1) Failure:
TestControllerTest#test_missing [test/controllers/test_controller_test.rb:6]:
[AbstractController::ActionNotFound] exception expected, not
Class: <ActionController::UrlGenerationError>
Message: <"No route matches {:action=>\"missing\", :controller=>\"test\"}">
---Backtrace---
test/controllers/test_controller_test.rb:7:in `block in test_missing'
test/controllers/test_controller_test.rb:6:in `test_missing'
---------------

The reason is because ActionController::TestCase is aware of the routes and won't allow calling an action that is not in the routes. But that is exactly what you are trying to test. And, I assume why you aren't using ActionController::TestCase.

At this point I wonder if you aren't testing something you shouldn't. Perhaps you should allow Rails to do its job and trust that it behaves correctly. But hey, we've come this far, why not just go all the way and test what Rails tests anyway. Instead of making the call through the full Rails app, let's try calling the TestController directly. If we create a new instance of the controller we can ask it to handle an action even if that action is not defined on the controller. But to do this we will have to dive deep into how ActionController works and make use of the AbstractController#process method:

require "test_helper"

class TestControllerTest < Minitest::Test
  def test_missing
    assert_raises AbstractController::ActionNotFound do
      TestController.new.process :missing
    end
  end
end

Now we are asking the controller to process an action that doesn't exist and testing that the controller behaves as expected. Yay?

What is the expected syntax for checking exception messages in MiniTest's assert_raises/must_raise?

You can use the assert_raises assertion, or the must_raise expectation.

it "must raise" do
  assert_raises RuntimeError do 
    bar.do_it
  end
  ->     { bar.do_it }.must_raise RuntimeError
  lambda { bar.do_it }.must_raise RuntimeError
  proc   { bar.do_it }.must_raise RuntimeError
end

If you need to test something on the error object, you can get it from the assertion or expectation like so:

describe "testing the error object" do
  it "as an assertion" do
    err = assert_raises RuntimeError { bar.do_it }
    assert_match /Foo/, err.message
  end

  it "as an exception" do
    err = ->{ bar.do_it }.must_raise RuntimeError
    err.message.must_match /Foo/
  end
end

How to assert that a Rails method will not throw a NoMethodError

You want to use assert_raise with the exception class you're expecting:

assert_raise(NoMethodError) { do_a_logout }

ETA: If you want to test that no error was raised, you can use assert_nothing_raised:

assert_nothing_raised { do_a_logout }
assert_nothing_raised(NoMethodError) { do_a_logout }

However as pointed out on SO and elsewhere, there is no good reason to use this assertion, because its redundant: you never expect an error to be raised, unless you specify otherwise.

Moreover, it gives a less helpful failure than simply running the spec without the assertion. In particular, running with assert_nothing_raised when an error occurs will give you a backtrace only to the assert_nothing_raised call, while running the spec without this assertion will give a backtrace to the actual error that's occurring.

minitest assert_select with capybara click_link

Firstly there is no need to assert on the presence of an element before clicking it since click_link will wait up to Capybara.default_max_wait_time seconds for the link to appear on the page and then click it. If the link doesn't appear in that time it will raise an error, so asserting on its presence is superfluous.

The error you're getting is because minitest-capybara isn't compatible with Capybara 2.9+ - https://github.com/wojtekmach/minitest-capybara/pull/17 - and the fact that assert_select doesn't take 2 strings as parameters. It just takes the id, name, or label text of a select element. So I'm guessing that's not actually the method you mean to be calling.

How to assert certain method is called with Ruby minitest framework?

With minitest you use expect method to set the expectation for a method to be called on a mock object like so

obj = MiniTest::Mock.new
obj.expect :right

If you want to set expectation with parameters and return values then:

obj.expect :right, return_value, parameters

And for the concrete object like so:

obj = SomeClass.new
assert_send([obj, :right, *parameters])

How to test if method gets called using MiniTest::Mock

You could do something like this:

  def test_if_bar_method_calls_puts
    mock = MiniTest::Mock.new
    mock.expect(:puts, nil, ['bar'])
    @class.stub :puts, -> (arg) { mock.puts arg } do
      @class.bar
    end
    assert mock.verify
  end

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