Units,Ruby: extend the test for mixin field

Units/parser-ruby.r/ruby-mixin-field.d/expected.tags

@@ -6,3 +6,11 @@ A	input.rb	/^class A$/;"	c	mixin:include:X,include:Y
 hi	input.rb	/^  def hi$/;"	f	class:A
 B	input.rb	/^class B$/;"	c	mixin:include:X
 prep	input.rb	/^  def self.prep$/;"	S	class:B
+C	input.rb	/^class C$/;"	c	mixin:prepend:X,prepend:Y
+hi	input.rb	/^  def hi$/;"	f	class:C
+D	input.rb	/^class D$/;"	c	mixin:prepend:X
+prep	input.rb	/^  def self.prep$/;"	S	class:D
+E	input.rb	/^class E$/;"	c	mixin:extend:X,extend:Y
+hi	input.rb	/^  def hi$/;"	f	class:E
+F	input.rb	/^class F$/;"	c	mixin:extend:X
+prep	input.rb	/^  def self.prep$/;"	S	class:F

Units/parser-ruby.r/ruby-mixin-field.d/input.rb

@@ -25,3 +25,31 @@ def self.prep
     include X
   end
 end
+
+class C
+  prepend X
+  def hi
+    p "Calling 'hi' in C."
+  end
+  prepend Y
+end
+
+class D
+  def self.prep
+    prepend X
+  end
+end
+
+class E
+  extend X
+  def hi
+    p "Calling 'hi' in E."
+  end
+  extend Y
+end
+
+class F
+  def self.prep
+    extend X
+  end
+end