modify 3d plot/ adding tests

pina/plotter.py

@@ -39,31 +39,33 @@ class Plotter:
             variables = problem.temporal_domain.variables
 
         if len(variables) not in [1, 2, 3]:
-            raise ValueError
+            raise ValueError('Samples can be plotted only in dimensions 1, 2 and 3.')
 
         fig = plt.figure()
         proj = '3d' if len(variables) == 3 else None
         ax = fig.add_subplot(projection=proj)
         for location in problem.input_pts:
             coords = problem.input_pts[location].extract(variables).T.detach()
-            if coords.shape[0] == 1:  # 1D samples
+            if len(variables)==1:  # 1D samples
                 ax.plot(coords.flatten(),
                         torch.zeros(coords.flatten().shape),
                         '.',
                         label=location,
                         **kwargs)
-            else:
+            elif len(variables)==2:
                 ax.plot(*coords, '.', label=location, **kwargs)
+            elif len(variables)==3:
+                ax.scatter(*coords, '.', label=location, **kwargs)
 
         ax.set_xlabel(variables[0])
         try:
             ax.set_ylabel(variables[1])
-        except:
+        except (IndexError, AttributeError):
             pass
 
         try:
             ax.set_zlabel(variables[2])
-        except:
+        except (IndexError, AttributeError):
             pass
 
         plt.legend()