Method MyException3

tests/test_exceptions.cpp:47–47

class MyException3 {
public:
    explicit MyException3(const char *m) : message{m} {}
    virtual const char *what() const noexcept { return message.c_str(); }
    // Rule of 5 BEGIN: to preempt compiler warnings.
    MyException3(const MyException3 &) = default;