$4.$ The following exercise is intended to encourage you to think of testing in a more rigorous way than you may be used to$.$ The exercise also hints at the strong relationship between specification clarity, faults, and test cases$1.$

a$.$ Write a Java method with the signature public static Vector union $($Vector a$,$ Vector b$).$ The method should return a Vector of objects that are in either of the two argument Vectors.

b$.$ Upon reflection, you may discover a variety of defects and ambiguities in the given assignment. In other words, ample opportunities for faults exist. Describe as many possible faults as you can. $($Note: Vector is a Java Collection class. If you are using another language, interpret Vector as a list.$)$

c$.$ Create a set of test cases that you think would have a reasonable chance of revealing the faults you identified above. Document a rationale for each test in