Subset matching broken on objects implementing to_hash and include?

Subject of the issue

rspec/rspec-expectations#1073 seems to break subset hash matching for objects implementing #to_hash and #include?. Previously these objects were converted using #to_hash on actual. Due to not converting to a Hash the check in comparing_hash_to_a_subset? will always be false and subset check won't be performed anymore (unless the objects #include? implements subset matching).

We had lots of breaking tests after the rspec-expectations patch update due to having specs on e.g. ActionDispatch::Response::Header like this:

expect(response.headers).to include 'Location' => 'http://test.host/...'

These expectations produced a nice diff when failing showing all send headers. We currently fixed it by explicitly calling #to_hash on these objects.

It would be nice if such use case could still be supported.

Your environment

• Ruby version: ruby 2.5.3p105 (2018-10-18 revision 65156) [x86_64-linux]
• rspec-expectations version: 3.8.2

Steps to reproduce

Run the following test case:

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  gem 'rspec-expectations', '3.8.2'
  gem 'minitest'
end

require 'rspec/matchers'

require 'minitest/autorun'

class CollectionLikeObject
  def to_hash
    {'Header' => 'Value'}
  end

  def include?(key)
    to_hash.include?(key)
  end
end

class IncludeTest < Minitest::Test
  def test_subset_match
    matcher = RSpec::Matchers::BuiltIn::Include.new('Header' => 'Value')
    actual  = CollectionLikeObject.new

    assert matcher.matches?(actual)
  end
end

Running the test case with 3.8.1 passes.

Expected behavior

I'd expect the expectations to still pass after a patch level upgrade.

Actual behavior

All expectations failed while showing a nice diff showing no difference.

Start with RSpec::Matchers::BuiltIn::Include and the comparing_hash_to_a_subset? check described in the issue. Run the provided Minitest reproduction against the affected and earlier rspec-expectations versions. Done means a to_hash-and-include? object passes the subset expectation and retains the expected failure diff behavior.