Method handleExpr

tutorials/external/catch.hpp:2190–2192

        template<typename T>
        void handleExpr( ExprLhs<T> const& expr ) {
            handleExpr( expr.makeUnaryExpr() );
        }
        void handleExpr( ITransientExpression const& expr );

        void handleMessage(ResultWas::OfType resultType, StringRef const& message);