fix test of global distance map

tests/test_flatland_envs_observations.py

@@ -41,7 +41,9 @@ def test_global_obs():
 
     # If this assertion is wrong, it means that the observation returned
     # places the agent on an empty cell
-    assert (np.sum(rail_map * global_obs[0][1][:, :, :4].sum(2)) > 0)
+    obs_agents_state = global_obs[0][1]
+    obs_agents_state = obs_agents_state + 1
+    assert (np.sum(rail_map * obs_agents_state[:, :, :4].sum(2)) > 0)
 
 
 def _step_along_shortest_path(env, obs_builder, rail):