Fix pneumatic node zero-flow reversal

tests/test_amesim_pneumatic_node_components.py

@@ -123,6 +123,37 @@ class AmesimPneumaticNodeComponentTests(unittest.TestCase):
         )
         self.assertAlmostEqual(energy_flow, 0.0, places=10)
 
+    def test_port_2_outflow_enthalpy_remains_finite_through_flow_reversal(self) -> None:
+        node = AmesimP4Node2("p4_1")
+        connected_h = {
+            "port_1": 300.0,
+            "port_2": 300.0,
+            "port_3": 200.0,
+            "port_4": 100.0,
+        }
+
+        outflow_enthalpies: list[float] = []
+        for reference_flow in (-1.0e-6, 0.0, 1.0e-6):
+            node.port_1.m_flow = -1.0
+            node.port_2.m_flow = reference_flow
+            node.port_3.m_flow = -reference_flow
+            node.port_4.m_flow = 1.0
+
+            node.update_stream_outflows(connected_h)
+
+            self.assertAlmostEqual(
+                sum(port.m_flow for port in node.ports.values()),
+                0.0,
+                places=15,
+            )
+            outflow_enthalpies.append(node.port_2.h_outflow)
+
+        self.assertTrue(all(abs(value) < 1.0e4 for value in outflow_enthalpies))
+        self.assertLess(
+            max(outflow_enthalpies) - min(outflow_enthalpies),
+            1.0,
+        )
+
 
 if __name__ == "__main__":
     unittest.main()