skip numba for dummy tests

tests/test_transform/test_tau_p.py

@@ -167,6 +167,7 @@ def test_coverage(self):
         """
         A small test of the jit'ed functions in python mode for coverage reasons.
         """
+        pytest.importorskip("numba")
         data = np.zeros((10, 10))
         dx = 1
         dt = 1