add spec for SortedSet being extracted from the set library

library/set/sortedset/new_spec.rb

@@ -0,0 +1,22 @@
+require_relative '../../../spec_helper'
+require 'set'
+
+ruby_version_is "3.0" do
+  describe "SortedSet.new" do
+    it "throws error including message that it has been extracted" do
+      -> {
+        SortedSet.new
+      }.should raise_error(RuntimeError) { |e|
+        e.message.should.include?("The `SortedSet` class has been extracted from the `set` library")
+      }
+    end
+  end
+end
+
+ruby_version_is ""..."3.0" do
+  describe "SortedSet.new" do
+    it "returns an instance of SortedSet" do
+      SortedSet.new.should be_an_instance_of(SortedSet)
+    end
+  end
+end