From 293ffb2bd35511ad84906aab8c71d88072494657 Mon Sep 17 00:00:00 2001
From: German Khokhlov <ouchlock@gmail.com>
Date: Tue, 3 Nov 2026 19:44:16 +0400
Subject: [PATCH] Pin that a stale GNSS zone and its refreshed neighbour stay
 apart and edge positions bin once

---
 src/layers/gnss/edgeCases.test.mjs | 97 ++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 src/layers/gnss/edgeCases.test.mjs

diff --git a/src/layers/gnss/edgeCases.test.mjs b/src/layers/gnss/edgeCases.test.mjs
new file mode 100644
index 000000000..a9155982f
--- /dev/null
+++ b/src/layers/gnss/edgeCases.test.mjs
@@ -0,0 +1,97 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import {
+  GNSS_CELL_DEG,
+  GNSS_WINDOW_MS,
+  accumulateGnssObservations,
+  binGnssCells,
+  gnssCellKey,
+  pruneGnssObservations,
+} from './records.js';
+
+const T0 = Date.UTC(2026, 0, 2, 12);
+const MINUTE = 60_000;
+const row = (hex, lat, lon, degraded) => ({ hex, lat, lon, degraded });
+// Cell edge shared by the two zones: 10.5° N.
+const SOUTH = 10.25;
+const NORTH = 10.75;
+
+const summary = (cells) =>
+  cells.map(({ id, aircraft, degraded, level }) => ({
+    id,
+    aircraft,
+    degraded,
+    level,
+  }));
+
+test('edge:gnss-integrity: a stale zone and its refreshed neighbour never mix', () => {
+  const store = new Map();
+  accumulateGnssObservations(
+    store,
+    [
+      row('aaa001', SOUTH, 20.2, true),
+      row('aaa002', SOUTH, 20.3, true),
+      row('aaa003', SOUTH, 20.4, false),
+    ],
+    T0,
+  );
+  // Twenty minutes later only the northern neighbour is refreshed; one
+  // degraded aircraft has crossed into it and now reports healthy.
+  accumulateGnssObservations(
+    store,
+    [
+      row('aaa001', NORTH, 20.2, false),
+      row('bbb001', NORTH, 20.3, false),
+      row('bbb002', NORTH, 20.4, false),
+    ],
+    T0 + 20 * MINUTE,
+  );
+  const southId = gnssCellKey(SOUTH, 20.2);
+  const northId = gnssCellKey(NORTH, 20.2);
+  assert.notEqual(southId, northId);
+  assert.deepEqual(
+    summary(binGnssCells(store)),
+    [
+      { id: southId, aircraft: 3, degraded: 2, level: 'high' },
+      { id: northId, aircraft: 3, degraded: 0, level: 'low' },
+    ].toSorted((a, b) => a.id.localeCompare(b.id)),
+  );
+
+  // Once the southern evidence leaves the window, only the fresh zone remains,
+  // unchanged: the stale zone's degraded reports do not leak into it.
+  pruneGnssObservations(store, T0 + GNSS_WINDOW_MS + MINUTE);
+  assert.deepEqual(summary(binGnssCells(store)), [
+    { id: northId, aircraft: 3, degraded: 0, level: 'low' },
+  ]);
+});
+
+test('edge:gnss-integrity: a position on the shared edge belongs to exactly one cell', () => {
+  const edge = 10.5;
+  const key = gnssCellKey(edge, 20.5);
+  // The edge belongs to the cell that starts there (north and east).
+  assert.equal(key, gnssCellKey(NORTH, 20.75));
+  assert.notEqual(key, gnssCellKey(SOUTH, 20.25));
+  for (let i = 0; i < 3; i++) assert.equal(gnssCellKey(edge, 20.5), key);
+
+  const store = new Map();
+  accumulateGnssObservations(
+    store,
+    [
+      row('ccc001', edge, 20.5, true),
+      row('ccc002', NORTH, 20.75, false),
+      row('ccc003', NORTH, 20.75, false),
+      row('ccc004', SOUTH, 20.25, false),
+      row('ccc005', SOUTH, 20.25, false),
+      row('ccc006', SOUTH, 20.25, false),
+    ],
+    T0,
+  );
+  const cells = binGnssCells(store);
+  const total = cells.reduce((sum, cell) => sum + cell.aircraft, 0);
+  assert.equal(total, 6);
+  const north = cells.find((cell) => cell.id === key);
+  assert.equal(north.aircraft, 3);
+  assert.equal(north.degraded, 1);
+  assert.equal(north.south, edge);
+  assert.equal(north.north, edge + GNSS_CELL_DEG);
+});