1..11
# ->initialize()
ok 1 - ->initialize() takes a mandatory callback parameter
ok 2 - ->initialize() takes a callable as a callback parameter
ok 3 - ->initialize() can take a function as a callback
ok 4 - ->initialize() can take an instance method as a callback
ok 5 - ->initialize() can take a static method as a callback
ok 6 - ->initialize() takes a custom message invalid_error
ok 7 - ->execute() changes $error with a custom message
# ->execute()
ok 8 - ->execute() returns true if callback returns true
ok 9 - ->execute() doesn't change $error if it returns true
ok 10 - ->execute() returns false if callback returns false
ok 11 - ->execute() changes $error with a default message if it returns false
 Looks like everything went fine.