Test external gems too.

Rakefile

@@ -3,7 +3,26 @@ require "rspec/core/rake_task"
 
 RSpec::Core::RakeTask.new(:test)
 
-task :default => :test
+task :default => [:test, :external]
+
+def clone_and_test(name)
+	sh("git clone https://git@github.com/socketry/#{name}")
+
+	# I tried using `bundle config --local local.async ../` but it simply doesn't work.
+	File.open("#{name}/Gemfile", "a") do |file| 
+		file.puts('gem "async", path: "../"')
+	end
+
+	sh("cd #{name} && bundle install && bundle exec rake test")
+end
+
+task :external do
+	Bundler.with_clean_env do
+		clone_and_test("async-io")
+		clone_and_test("async-websocket")
+		clone_and_test("falcon")
+	end
+end
 
 task :coverage do
 	ENV['COVERAGE'] = 'y'