tests.test_plot: allow running module standalone.

This allows the module to be invoked using 'python3 -m tests.test_plot'.

Author: Benjamin Moody

tests/test_plot.py

@@ -43,3 +43,7 @@ def test_create_figure_multiple_subplots(self):
         assert fig is not None
         assert axes is not None
         assert len(axes) == n_subplots
+
+
+if __name__ == "__main__":
+    unittest.main()