[Year 12 SofDev] Test data question

[Frank Van Den Boom]

A couple of the VITTA sample papers have had the following type of question where students are asked to suggest three values that should be used to test an if statement like the following.
 
if x > 50 then
....
else
....
endif
 
I have no issue with boundary values 49 and 50 being essential. It's the third one I have a problem with. 
The solutions say "when testing an algorithm, always select values that are within the required range, at the boundary of the required range, and outside of the required range". So for the above code, the solution suggests using 49, 50, 51.
 
I don't see that 51 is telling us any more than 50, so I don't really consider it useful test data and have taught my kids to also include invalid data types as part of this testing. eg. "apple" I guess it depends on how/where data input features in the code being tested.
 
What do others think about this?
 
Frank

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