Hacker News Reader

How do you generate the test cases? Check the types being fed in and fed out, then generate random input/output scenarios?

View on HN

It's pretty simple. I'm decoding a structure into bit fields (802.11 Information Element). I have a hex dump that I decode into a two structures with almost 100 fields (eyeroll for 802.11 committee). Each field can only be 0, 1, or sometimes up to 15.

I have a list of the structure members. I generate an assert for each member being a certain value. The python script builds/runs the C code. On failure, I parse the assertion failure, get the actual value, change the C assert string, rebuild-rerun. Continue until the program succeeds.

I've visually verified the decode is correct once. I want to keep the decoder tested if I change the code again so I'm generating complete test coverage.

It sounds like your use case is property based testing. Have you tried any of the QuickCheck ports to C++? My favorite is RapidCheck (https://github.com/emil-e/rapidcheck). You define generators for your struct fields and write a pure function to check whether the parsed output conforms to your expectations.

Checking that out now! Reminds me a little of the Python library Hypothesis. https://hypothesis.readthedocs.io/en/latest/

Reply on news.ycombinator.com