text: #define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
  #include "doctest.h"
  
  int factorial(int number) { return number <= 1 ? number : factorial(number - 1) * number; }
  
  TEST_CASE("testing the factorial function")
  {
      CHECK(factorial(1) == 1);
      CHECK(factorial(2) == 2);
      CHECK(factorial(3) == 6);
      CHECK(factorial(10) == 3628800);
  }
  