Move spec under Module#undef_method since there is no Class#undef_method

Author: eregon

spec/ruby/core/class/undef_method_spec.rb

@@ -56,13 +56,21 @@ def another_method_to_undef() 1 end
     @module.send(:undef_method, :method_to_undef).should equal(@module)
   end
 
-  it "raises a NameError when passed a missing name" do
+  it "raises a NameError when passed a missing name for a module" do
     -> { @module.send :undef_method, :not_exist }.should raise_error(NameError, /undefined method `not_exist' for module/) { |e|
       # a NameError and not a NoMethodError
       e.class.should == NameError
     }
   end
 
+  it "raises a NameError when passed a missing name for a class" do
+    klass = Class.new
+    -> { klass.send :undef_method, :not_exist }.should raise_error(NameError, /undefined method `not_exist' for class/) { |e|
+      # a NameError and not a NoMethodError
+      e.class.should == NameError
+    }
+  end
+
   describe "on frozen instance" do
     before :each do
       @frozen = @module.dup.freeze