unit testing an object that takes a "traits" template parameter

I have a Visual Studio 2008 C++03 project where I would like to unit test a class that uses a traits template parameter that exposes static methods (Policy-based design, strategy pattern). I am using Google Test and Google Mock frameworks.

For example:

/// the class under test
template< typename FooTraits >
class Foo
    void DoSomething()
        FooTraits::handle_type h = FooTraits::Open( "Foo" );
        /* ... */
        FooTraits::Close( h );

/// a typical traits structure
struct SomeTraits
    typedef HANDLE handle_type;
    static handle_type Open( const char* name ) { /* ... */ };
    static void Close( handle_type h ) { /* ... */ };

/// mocked traits that I would like to use for testing
struct MockTraits
    typedef int handle_type;
    static MOCK_METHOD1( Open, handle_type( const char* ) );
    static MOCK_METHOD1( Close, void( handle_type ) );

/// the test function
TEST( FooTest, VerifyDoSomethingWorks )
    Foo< MockTraits > foo_under_test;

    // expect MockTraits::Open is called once
    // expect MockTraits::Close is called once with the parameter returned from Open

Obviously this won't work as-is. Google Mock can't mock static methods and I would need to create an instance of the Mocked class in the test to set its behavior and expectations.

So what is the correct way to unit test a class that accepts a template policy using Google Test / Google Mock?


Can you make a class with non-static methods, create a global instance of it (or static in your traits), and have your traits class defer to it?

So, to clarify the idea that was inspired by Rob's comment:

struct FunnyDoodad

   MOCK_METHOD1( Open, HANDLE( const char* ) );
   MOCK_METHOD1( Close, void( handle_type ) );


struct FunnyGlobal {
  FunnyGlobal() : pimpl() {}
  ~FunnyGlobal() { delete pimpl; }

  // You'd want some protection here rather than just dereferencing.
  // it's the whole point.  I'd suggest using whatever unit test assertion
  // mechanism your framework uses and make it a fatal check.    
  handle_type Open(char const* name) { return pimpl->Open(name); }
  void Close(handle_type h) { pimpl->Close(h); }
   FunnyDoodad * pimpl;

  friend struct FunnyDoodad;

  void register(FunnyDoodad* p) { pimpl = p; }
  void deregister() { pimpl = 0; }

FunnyGlobal funnyGlobal;

FunnyDoodad::FunnyDoodad() { funnyGlobal.register(this); }
FunnyDoodad::~FunnyDoodad() { funnyGlobal.deregister(); }

struct TestTraits
    typedef HANDLE handle_type;
    static handle_type Open( const char* name ) { return funnyGlobal.Open(name); };
    static void Close( handle_type h ) { funnyGlobal.Close(h); };

   FunnyDoodad testDoodad;


I imagine the above could be templated and almost turned into a pattern...maybe.

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