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tests/test_tank.py

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+# tests/test_tank.py
+import numpy as np
+import pytest
+from tank import Tank
+
+
+GAMMA = 1.4
+R_GAS = 287.0
+
+
+def test_tank_initial_state_matches_ideal_gas():
+    """
+    Given P, T, V construct a Tank; mass and U should match ideal gas:
+      rho  = P / (R * T)
+      mass = rho * V
+      U    = P * V / (gamma - 1)     (since u=0 inside tank)
+      T    = (U / mass) * (gamma - 1) / R   (round-trip)
+    """
+    tank = Tank(V=5.0, P_init=10e6, T_init=300.0, gamma=GAMMA, R_gas=R_GAS)
+    rho_expected = 10e6 / (R_GAS * 300.0)
+    assert abs(tank.rho - rho_expected) < 1e-9
+    assert abs(tank.mass - rho_expected * 5.0) < 1e-6
+    assert abs(tank.U - 10e6 * 5.0 / (GAMMA - 1)) < 1e-3
+    assert abs(tank.P - 10e6) < 1e-3
+    assert abs(tank.T - 300.0) < 1e-9
+
+
+def test_tank_ghost_state_is_stagnation_conservative_vector():
+    """
+    ghost_state() should return [rho, 0, P/(gamma-1)]
+    (u_ghost = 0 per spec §2.3, so total energy density equals
+    internal energy density = P/(gamma-1)).
+    """
+    tank = Tank(V=5.0, P_init=10e6, T_init=300.0, gamma=GAMMA, R_gas=R_GAS)
+    g = tank.ghost_state()
+    assert g.shape == (3,)
+    assert abs(g[0] - tank.rho) < 1e-12
+    assert g[1] == 0.0
+    assert abs(g[2] - 10e6 / (GAMMA - 1)) < 1e-3
+
+
+def test_tank_apply_flux_outflow_reduces_mass_energy_and_pressure():
+    """
+    apply_flux(mdot, edot, dt, sign=-1) should subtract mdot*dt from mass
+    and edot*dt from U. Derived P should decrease correspondingly.
+    """
+    tank = Tank(V=5.0, P_init=10e6, T_init=300.0, gamma=GAMMA, R_gas=R_GAS)
+    mass_before = tank.mass
+    U_before = tank.U
+    P_before = tank.P
+    mdot = 1.0      # kg/s
+    edot = 5e5      # J/s (enthalpy rate)
+    dt = 1e-3
+    tank.apply_flux(mdot=mdot, edot=edot, dt=dt, sign=-1)
+    assert abs(tank.mass - (mass_before - mdot * dt)) < 1e-12
+    assert abs(tank.U    - (U_before    - edot * dt)) < 1e-9
+    assert tank.P < P_before