[susshshshah]

How do you know what tests to write if you don’t understand the code?

[9rx]

Same way you normally would? Tests are concerned with behaviour. The code that implements the behaviour is immaterial.

[wiseowise]

How do you do TDD without having code in the first place? How do QA verifies without reading the source?

[adastra22]

I’m not sure I understand this statement. You give your program parameters X and expect result Y, but instead get Z. There is your test, embedded in the problem statement.