make comprehensive test more comprehensive

kwant/tests/test_comprehensive.py

@@ -51,5 +51,7 @@ def test_qhe(W=16, L=8):
                                        ((5.2, 5.5), 3, 1e-1)]:
         for r_phi in r_phis:
             args = (1.0 / r_phi, "")
-            T_actual = kwant.smatrix(sys, 1.0, args).transmission(1, 0)
-            assert abs(T_nominal - T_actual) < max_err
+            pc = sys.precalculate(1.0, args)
+            for result in [kwant.smatrix(pc, 1, args),
+                           kwant.solvers.default.greens_function(pc, 1, args)]:
+                assert abs(T_nominal - result.transmission(1, 0)) < max_err