The unit_test_log_formatter class encapsulates formatting of log events for an output stream.

namespace boost { namespace unit_test {

class BOOST_TEST_DECL unit_test_log_formatter {
public:
    enum log_entry_types { BOOST_UTL_ET_INFO,
                           BOOST_UTL_ET_MESSAGE,
                           BOOST_UTL_ET_WARNING,
                           BOOST_UTL_ET_ERROR,
                           BOOST_UTL_ET_FATAL_ERROR };

    // Destructor
    virtual             ~unit_test_log_formatter() {}

    // Formatter interface
    virtual void        log_start( std::ostream&, counter_t test_cases_amount ) = 0;
    virtual void        log_finish( std::ostream& ) = 0;
    virtual void        log_build_info( std::ostream& ) = 0;

    virtual void        test_unit_start( std::ostream&, test_unit const& tu ) = 0;
    virtual void        test_unit_finish( std::ostream&, test_unit const& tu, unsigned long elapsed ) = 0;
    virtual void        test_unit_skipped( std::ostream&, test_unit const& ) = 0;

    virtual void        log_exception( std::ostream& os, log_checkpoint_data const& cd, execution_exception const& ex )
    {
        // for backward compatibility
        log_exception( os, cd, ex.what() );
    }
    virtual void        log_exception( std::ostream&, log_checkpoint_data const&, const_string /* explanation */ ) {}

    virtual void        log_entry_start( std::ostream&, log_entry_data const&, log_entry_types let ) = 0;
    virtual void        log_entry_value( std::ostream&, const_string value ) = 0;
    virtual void        log_entry_value( std::ostream&, lazy_ostream const& value ); // there is a default impl
    virtual void        log_entry_finish( std::ostream& ) = 0;
};

} }