Add specs for [Feature #13983] Rational and Complex should be frozen

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@60505 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

spec/ruby/core/kernel/freeze_spec.rb

@@ -51,6 +51,24 @@ describe "Kernel#freeze" do
     end
   end
 
+  ruby_version_is "2.5" do
+    describe "on a Complex" do
+      it "has no effect since it is already frozen" do
+        c = Complex(1.3, 3.1)
+        c.frozen?.should be_true
+        c.freeze
+      end
+    end
+
+    describe "on a Rational" do
+      it "has no effect since it is already frozen" do
+        r = Rational(1, 3)
+        r.frozen?.should be_true
+        r.freeze
+      end
+    end
+  end
+
   it "causes mutative calls to raise RuntimeError" do
     o = Class.new do
       def mutate; @foo = 1; end