redo and move rover ranking a little

server/src/services/assignmentService/roverRanking.test.js

@@ -0,0 +1,69 @@
+// Rover assignment ranking tests
+// Purpose: Locks the operator-defined rover priority order against accidental comparator regressions.
+// Scope: Tests pure ranking only; assignment side effects and access policy remain owned by their existing services.
+const test = require('node:test');
+const assert = require('node:assert/strict');
+const { compareRoversForAssignment } = require('./roverRanking');
+
+function rover({ id, docked, battery, drivers = 0 }) {
+  /*
+    Set size matches the production rover contract without introducing socket or
+    rover-manager dependencies into these focused ordering tests.
+  */
+  return {
+    id,
+    docked,
+    batteryState: battery == null ? null : { percentDisplay: battery },
+    drivers: new Set(Array.from({ length: drivers }, (_, index) => `${id}-driver-${index}`)),
+  };
+}
+
+function rankedIds(entries) {
+  return entries.sort(compareRoversForAssignment).map((entry) => entry.id);
+}
+
+test('an undocked empty rover outranks every rover that is docked or occupied', () => {
+  const result = rankedIds([
+    rover({ id: 'occupied-high', docked: false, battery: 100, drivers: 1 }),
+    rover({ id: 'docked-high', docked: true, battery: 100 }),
+    rover({ id: 'ready-empty', docked: false, battery: 20 }),
+  ]);
+
+  assert.equal(result[0], 'ready-empty');
+});
+
+test('battery percentage ranks rovers after undocked-and-empty readiness', () => {
+  const result = rankedIds([
+    rover({ id: 'low', docked: false, battery: 35 }),
+    rover({ id: 'high', docked: false, battery: 90 }),
+    rover({ id: 'middle', docked: false, battery: 60 }),
+  ]);
+
+  assert.deepEqual(result, ['high', 'middle', 'low']);
+});
+
+test('known battery percentage outranks missing battery telemetry', () => {
+  const result = rankedIds([
+    rover({ id: 'unknown', docked: true, battery: null }),
+    rover({ id: 'known', docked: true, battery: 5 }),
+  ]);
+
+  assert.deepEqual(result, ['known', 'unknown']);
+});
+
+test('driver count breaks a battery-percentage tie', () => {
+  const result = rankedIds([
+    rover({ id: 'busy', docked: false, battery: 70, drivers: 3 }),
+    rover({ id: 'less-busy', docked: false, battery: 70, drivers: 1 }),
+  ]);
+
+  assert.deepEqual(result, ['less-busy', 'busy']);
+});
+
+test('exactly equivalent rovers remain tied for random selection by assignmentService', () => {
+  const left = rover({ id: 'left', docked: false, battery: 80, drivers: 1 });
+  const right = rover({ id: 'right', docked: false, battery: 80, drivers: 1 });
+
+  assert.equal(compareRoversForAssignment(left, right), 0);
+  assert.equal(compareRoversForAssignment(right, left), 0);
+});