Create and export Stack constructor
Add tests for initial conditions
Add tests for Stack#getSize and Stack#isEmpty
Add tests for Stack#push and Stack#peek
Add tests for Stack#pop
Add test for Stack#clear
Implement Stack#push and Stack#isEmpty
Fix typo
Implement Stack#clear
Fix typo
Implement Stack#getSize
Implement Stack#peek
Add tests to Stack#pop and Stack#peek
Implement Stack#pop
Fix test for Stack#clear
Fix test for Stack#peek