Should I make a member function virtual just to make the class testable?

I am working on a class whose simplified version looks like this:

class Http_server {
public:
    void start(int port)
    {
        start_server();
        std::string content_type = extract_content_type(get_request());
    }

private:
    void start_server()
    {
        ...
    }

    std::string get_request()
    {
        ...
    }

    std::string extract_content_type(const std::string& request) const
    {
        ...
    }
};

Now I want to write a test case for extract_content_type. The problem is that it is closed, so I can not call it from the outside. The only function I can test is start, but it will actually start the server ( start_server) and wait for the request ( get_request).

As I can see, I have three options:

• Make extract_content_typepublic
• Extract extract_content_typeto utility class or namespace
• Make start_serverit get_requestvirtual and create a mock object that overrides them.

- , , 3.

V8: http://code.google.com/p/v8/source/browse/trunk/test/cctest/test-date.cc

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