using new strategy for marking slow tests

test.py

@@ -52,7 +52,7 @@ def test_matvec(ctx_factory):
     compare.arrays(a@b, c)
 
 
-@pytest.mark.skip("slow")
+@pytest.mark.slow
 def test_compute_flux_derivatives(ctx_factory):
     queue = device.get_queue(ctx_factory)
     prg = program.get_weno()
@@ -64,7 +64,7 @@ def test_compute_flux_derivatives(ctx_factory):
     kernel.compute_flux_derivatives(queue, prg, params, arrays)
 
 
-@pytest.mark.skip("slow")
+@pytest.mark.slow
 def test_compute_flux_derivatives_gpu(ctx_factory):
     queue = device.get_queue(ctx_factory)
     prg = program.get_weno()