When an expect_raises assertion fails, the expected message goes through #pretty_inspect but the actual message doesn't:

This leads to some confusing situations where the two messages look identical if, for example, the actual message is already the #inspect form of the expected message:

require "spec"

it do
  expect_raises(Exception, %q(a\tb\nc)) do
    raise %q(a\tb\nc).inspect
  end
end

Failures:

  1) assert
     Failure/Error: expect_raises(Exception, %q(a\tb\nc)) do

       Expected Exception with "a\\tb\\nc", got #<Exception: "a\\tb\\nc"> with backtrace:
...

We should make the failure less ambiguous here.