Test function for the gradient

Dear all,

I was reading the documentation and I couldn't find the answer for this question:

Assume that you are using P1 elements to discretize your solution with respect to the space (2D). Your solution takes zero value at the boundary, but the y derivative uy doesn't. what are the test functions that comsol uses to compute the integral of (uy)^2 over the boundary?

Note: I'm assuming that, once comsol has a solution u (and uy) and we want to integrate it (for instance using the "derived values"), the galerkin approximation u_h=sum u_i Phi_i is used.

Thank you in advance!