add readme example to regression test

fglib/tests/test_inference.py

@@ -134,5 +134,55 @@ def test_msa(self):
         pass
 
 
+class TestExample(unittest.TestCase):
+
+    def test_readme(self):
+        # Create factor graph
+        fg = graphs.FactorGraph()
+
+        # Create variable nodes
+        x1 = nodes.VNode("x1", rv.Discrete)  # with 2 states (Bernoulli)
+        x2 = nodes.VNode("x2", rv.Discrete)  # with 3 states
+        x3 = nodes.VNode("x3", rv.Discrete)
+        x4 = nodes.VNode("x4", rv.Discrete)
+
+        # Create factor nodes (with joint distributions)
+        dist_fa = [[0.3, 0.2, 0.1],
+                   [0.3, 0.0, 0.1]]
+        fa = nodes.FNode("fa", rv.Discrete(dist_fa, x1, x2))
+
+        dist_fb = [[0.3, 0.2],
+                   [0.3, 0.0],
+                   [0.1, 0.1]]
+        fb = nodes.FNode("fb", rv.Discrete(dist_fb, x2, x3))
+
+        dist_fc = [[0.3, 0.2],
+                   [0.3, 0.0],
+                   [0.1, 0.1]]
+        fc = nodes.FNode("fc", rv.Discrete(dist_fc, x2, x4))
+
+        # Add nodes to factor graph
+        fg.set_nodes([x1, x2, x3, x4])
+        fg.set_nodes([fa, fb, fc])
+
+        # Add edges to factor graph
+        fg.set_edge(x1, fa)
+        fg.set_edge(fa, x2)
+        fg.set_edge(x2, fb)
+        fg.set_edge(fb, x3)
+        fg.set_edge(x2, fc)
+        fg.set_edge(fc, x4)
+
+        # Perform sum-product algorithm on factor graph
+        # and request belief of variable node x4
+        belief = inference.sum_product(fg, x4)
+
+        # Print belief of variables
+        # print("Belief of variable node x4:")
+        # print(belief)
+
+        npt.assert_almost_equal(belief.pmf, np.array([0.63, 0.36]), decimal=2)
+
+
 if __name__ == "__main__":
     unittest.main()