Fix assertions on exception messages

[KnVerey]

I realized while working on a feature on this repo that we've been misusing assert_raises. We have a bunch of tests that assume the second arg will be asserted as the error message, whereas it is in fact just used as the assertion failure message. I wrote most of these mistakes myself, but I don't think I'm the only one with the misimpression (it was actually originally suggested to me by a reviewer). This PR fixes the misuse, introduces a helper with the desired behaviour, and tries to prevent future confusion.

[kirs]

Personally I always use

error = assert_raises(MyError) {}
assert_match(/message/, error.to_s

But I see the point of assert_raises_msg and how it could be useful.

[kirs]

I see the value of the override but we should keep it mind that we could no longer use the last argument feature (http://www.rubydoc.info/gems/minitest/5.10.1/Minitest/Assertions#assert_raises-instance_method):

assert_raises(WhateverError, "does not raise when logging is disabled") { ... }

[KnVerey]

I see the value of the override but we should keep it mind that we could no longer use the last argument feature

True, and it would be easy enough to make that possible. Pushed another commit that lets you use a kwarg if you're using that feature on purpose. LMK what you think. Here are some examples:

  def test_assert_raises
    assert_raises(StandardError, "foobar") do
    end
  end

  1) Failure:
RunnerTest#test_assert_raises [test/unit/kubernetes-deploy/runner_test.rb:10]:
Please use assert_raises_msg to check the exception message,
or use the msg keyword argument to specify a message to use when the assertion fails.

  def test_assert_raises
    assert_raises(StandardError, msg: "This is an error message.") do
    end
  end

  1) Failure:
RunnerTest#test_assert_raises [test/unit/kubernetes-deploy/runner_test.rb:10]:
This is an error message.
StandardError expected but nothing was raised.

  def test_assert_raises
    assert_raises(StandardError) do
    end
  end

  1) Failure:
RunnerTest#test_assert_raises [test/unit/kubernetes-deploy/runner_test.rb:10]:
StandardError expected but nothing was raised.

[kirs]

Great idea!
What about using message instead of msg? That would keep parity with other test helpers at Shopify that use message as a keyword argument.

[KnVerey]

Pushed another commit that makes this a duplicate of what I just proposed in core.

[kirs]

🚢