Checks that constructors and assignment operators marked as = default are not actually deleted by the compiler.

class Example {
  // This constructor is deleted because I is missing a default value.
  Example() = default;
  // This is fine.
  Example(const Example& Other) = default;
  // This operator is deleted because I cannot be assigned (it is const).
  Example& operator=(const Example& Other) = default;

  const int I;