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tests/cryo_tank/test_properties.py

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+# tests/cryo_tank/test_properties.py
+"""Tests for CoolProp property wrappers."""
+import pytest
+import sys
+sys.path.insert(0, "src")
+
+from cryo_tank.properties import (
+    ln2_rho, ln2_h, ln2_u, ln2_T_from_u,
+    n2_vapor_u, n2_sat_pressure,
+    he_u, he_h, he_cp, he_cv,
+)
+from cryo_tank.config import P_WORKING
+
+
+class TestLN2Properties:
+    """Liquid nitrogen properties at P = 0.17 MPa."""
+
+    def test_ln2_density_at_78K(self):
+        rho = ln2_rho(78.0, P_WORKING)
+        assert 800 < rho < 810  # ~803 kg/m3
+
+    def test_ln2_enthalpy_at_77K(self):
+        h = ln2_h(77.0, P_WORKING)
+        assert -130000 < h < -110000  # ~-122695 J/kg
+
+    def test_ln2_internal_energy_at_78K(self):
+        u = ln2_u(78.0, P_WORKING)
+        assert -130000 < u < -110000  # ~-120865 J/kg
+
+    def test_ln2_T_from_u_roundtrip(self):
+        T_orig = 78.0
+        u = ln2_u(T_orig, P_WORKING)
+        T_recovered = ln2_T_from_u(u, P_WORKING)
+        assert abs(T_recovered - T_orig) < 0.01
+
+
+class TestN2VaporProperties:
+    """N2 vapor properties."""
+
+    def test_n2_sat_pressure_at_78K(self):
+        P_sat = n2_sat_pressure(78.0)
+        assert 0.10e6 < P_sat < 0.12e6  # ~0.1093 MPa
+
+    def test_n2_vapor_internal_energy_at_78K(self):
+        u = n2_vapor_u(78.0)
+        assert 50000 < u < 60000  # ~55547 J/kg
+
+
+class TestHeliumProperties:
+    """Helium (ideal gas) properties."""
+
+    def test_he_cp_near_5196(self):
+        cp = he_cp()
+        assert abs(cp - 5196.2) < 10  # monatomic ideal gas
+
+    def test_he_cv_near_3117(self):
+        cv = he_cv()
+        assert abs(cv - 3117.1) < 10
+
+    def test_he_enthalpy_at_100K(self):
+        h = he_h(100.0)
+        # CoolProp gives ~524762 J/kg at 100K
+        assert 500000 < h < 550000
+
+    def test_he_internal_energy_at_78K(self):
+        u = he_u(78.0)
+        assert 200000 < u < 280000  # ~247932 J/kg