I've taken online classes where they give you unit tests that use one set of inputs/outputs, when grading they'd use the same tests, but have a different set of

I've taken online classes where they give you unit tests that use one set of inputs/outputs, when grading they'd use the same tests, but have a different set of inputs/outputs. Early on there was one or two cases where subtle problems came up because the public set and private set accidentally tested things slightly differently, but the TA / prof was quick to respond.