Add test for `plot_traj.py`

Trajectories/Tests/tests.json

@@ -107,5 +107,16 @@
 	    "$PWD/Eurec4A_graph_anti/segments_cost_functions.gt",
 	    "segments.gv", "-t", "$PWD/Eurec4A_graph_anti/traj_segm.json"
 	]
+    },
+    {
+	"title": "Plot_traj",
+	"command":
+	[
+	    "$src_dir/Trajectories/plot_traj.py",
+	    "$tests_old_dir/Trajectories/expanded_traj.json",
+	    "$tests_old_dir/Cost_functions/e_overestim.txt",
+	    "$tests_old_dir/Extraction_eddies_region_2_noise/SHPC",
+	    "Anticyclones"
+	]
     }
 ]