Add spec for memsize of typed data struct.

Author: aardvark179

spec/ruby/optional/capi/ext/typed_data_spec.c

@@ -43,7 +43,11 @@ void sample_typed_wrapped_struct_mark(void* st) {
 }
 
 size_t sample_typed_wrapped_struct_memsize(const void* st) {
-  return sizeof(struct sample_typed_wrapped_struct);
+  if (st == NULL) {
+    return 0;
+  } else {
+    return ((struct sample_typed_wrapped_struct *)st)->foo;
+  }
 }
 
 static const rb_data_type_t sample_typed_wrapped_struct_data_type = {

spec/ruby/optional/capi/typed_data_spec.rb

@@ -1,4 +1,5 @@
 require_relative 'spec_helper'
+require 'objspace'
 
 load_extension("typed_data")
 
@@ -7,6 +8,11 @@
     @s = CApiAllocTypedSpecs.new
     @s.typed_wrapped_data.should == 42 # not defined in initialize
   end
+
+  it "uses the specified memsize function for ObjectSpace.memsize" do
+    @s = CApiAllocTypedSpecs.new
+    ObjectSpace.memsize_of(@s).should > 42
+  end
 end
 
 describe "CApiWrappedTypedStruct" do