Add assertion to README.md testing block.

[simi]

Rails 7.2 introduced warning for assertion-free tests. Good to recommend block with assertion (similar to rspec one) to prevent warnings.

[debano]

assert_nothing_raised does not appear to be actually rescuing the exceptions raised by BetterHtml.

I'm exploring something like this (with additional handling since not all BetterHtml errors inherit from the same base class)

test "html errors in #{pathname}" do
  data = File.read(filename)

  begin
    BetterHtml::BetterErb::ErubiImplementation.new(data, filename:).validate!
    assert(true, "No exception was raised")
  rescue RuntimeError => e
    # Not all BetterHtml errors inherit from a common base class, so we need to check for module the prefix
    if e.class.name.start_with?("BetterHtml::")
      flunk("BetterHTML exception raised: #{e.class} - #{e.message}")
    else
      raise e
    end
  end
end

[simi]

It seems RuntimeError based exception is raised for invalid input on purpose.