This question is based on black-box software testing techniques.
1.A. Write a brief functional description for the function.
1.B. Generate functional test cases based on the functional description.
1.C. Identify and specify the equivalence partitions and generate equivalence partitioning test cases.
1.D. Generate boundary value analysis test cases.
1.E. Write an actual program to implement the average function in any programming language. Apply the boundary value analysis test cases you’ve suggested in D.