before functional changes by codex

test/integration/pfr-boundary.integration.test.js

@@ -0,0 +1,35 @@
+const test = require('node:test');
+const assert = require('node:assert/strict');
+
+const { Reactor_PFR } = require('../../src/specificClass');
+const { makeReactorConfig } = require('../helpers/factories');
+
+test('_applyBoundaryConditions enforces Danckwerts inlet and Neumann outlet for flowing case', () => {
+  const reactor = new Reactor_PFR(
+    makeReactorConfig({ reactor_type: 'PFR', n_inlets: 1, length: 10, resolution_L: 5, volume: 50, alpha: 0.2 }),
+  );
+
+  reactor.Fs[0] = 2;
+  reactor.Cs_in[0] = Array(13).fill(9);
+  reactor.D = 1;
+
+  const state = Array.from({ length: reactor.n_x }, (_, i) => Array(13).fill(i));
+  reactor._applyBoundaryConditions(state);
+
+  assert.deepEqual(state[reactor.n_x - 1], state[reactor.n_x - 2]);
+  assert.equal(state[0].every((v) => Number.isFinite(v)), true);
+});
+
+test('_applyBoundaryConditions copies first interior slice when no flow is present', () => {
+  const reactor = new Reactor_PFR(
+    makeReactorConfig({ reactor_type: 'PFR', n_inlets: 1, length: 10, resolution_L: 5, volume: 50 }),
+  );
+
+  reactor.Fs[0] = 0;
+  const state = Array.from({ length: reactor.n_x }, (_, i) => Array(13).fill(i + 10));
+
+  reactor._applyBoundaryConditions(state);
+
+  assert.deepEqual(state[0], state[1]);
+  assert.deepEqual(state[reactor.n_x - 1], state[reactor.n_x - 2]);
+});