Module testing of MyStack_witherrors.class

Verification of all of the methods at MyStack_witherrors.class using JUnit4. The testing identified that method peek() does not correct work, it give null at all of the cases. Also, can not be testing correctly method pop() and push() with out correcting method peek(). You also can find new corrected MyStack_witherrors.class at file MyStack.class, and module tests for them at MyStack_tests.class.