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 RuntimeErrorend

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/  endend

To assert exception:

assert_raises FooError do  bar.do_itend

To assert exception message:

As per API doc, assert_raises returns the exception matched so you can check the message, attributes, etc.

exception = assert_raises FooError do  bar.do_itendassert_equal('Foo', exception.message)

Minitest does not provide (yet) you a way to check the actual exception message. But you could add a helper method that does it and extend ActiveSupport::TestCase class to use everywhere in your rails test suite, e.g.:in test_helper.rb

class ActiveSupport::TestCase  def assert_raises_with_message(exception, msg, &block)    block.call  rescue exception => e    assert_match msg, e.message  else    raise "Expected to raise #{exception} w/ message #{msg}, none raised"  endend

and use it in your tests like:

assert_raises_with_message RuntimeError, 'Foo' do  code_that_raises_RuntimeError_with_Foo_messageend