First test case is failing, I have tried checking the shape and using a_prev_pad inside loop for assigning a_slice_prev
Check whether you are using stride correctly when you compute the start and end indices.
Exactly as Tom says, there is a problem with how you are handling the stride. The fact that your Z[0,2,1] value is zero most likely means that you included the stride as a “step” in the “range” expression of the for loops over h and w. That is a mistake. The for loops are over the output space and you must touch every value there and not skip any. The striding happens in the input space. So at each iteration of the loops you use the stride value to calculate vert_start and horiz_start in the input space.