onegridequivalencetest fails
This test computes the mortar transformation for two grids with conforming contact boundary and compares the resulting mortar-transformed entries in the stiffness matrix to the stiffness entries of a grid which is the union of both contacting grids. I am not sure yet if the entries have to be same in the case of dual/Lagrange mortar functions or if this test is just an ancient test for a pointwise coupling