Test data could be below possible values; 1. Fib(0) - this should return 0 2. Fib(1) - this should return 0 1 3. Fib(2) - this should return 0 1 1 Now if there is any size limit mentioned, prepare test data around the size Assume if size mentioned in the program is 6 4. Fib(6) - 0 1 1 2 3 5 5. Fib(size-1) i.e Fib(5) - 0 1 1 2 3 6. Fib(size + 1) - depending on the program, it should return result Negative Scenario's 7.Fib(2.3) - see if program can either convert this into 2(chopping the decimal/ or throws error) 8. Fib(-1) - output -1 Hope this helps !