use force model keyword

lbmpy_tests/test_force.py

@@ -177,7 +177,7 @@ def test_momentum_density_shift(force_model):
     src = dh.add_array('src', values_per_cell=len(stencil))
     dh.fill('src', 0.0, ghost_layers=True)
 
-    method = create_lb_method(method="srt", compressible=True, force_model='guo', force=[1, 2])
+    method = create_lb_method(method="srt", compressible=True, force_model=force_model, force=[1, 2])
 
     momentum_density_symbols = sp.symbols("md_:2")
     cqc = method.conserved_quantity_computation