Add more test coverage

src/engine/EntityManager.ts

@@ -5,13 +5,16 @@ export class EntityManager {
   private grid: Map<number, EntityId[]> = new Map();
   private actors: Map<EntityId, Actor>;
   private world: World;
+  private lastId: number = 0;
 
   constructor(world: World) {
     this.world = world;
     this.actors = world.actors;
+    this.lastId = Math.max(0, ...this.actors.keys());
     this.rebuildGrid();
   }
 
+
   rebuildGrid() {
     this.grid.clear();
     for (const actor of this.actors.values()) {
@@ -77,6 +80,8 @@ export class EntityManager {
     }
   }
 
+
+
   getActorsAt(x: number, y: number): Actor[] {
     const i = idx(this.world, x, y);
     const ids = this.grid.get(i);
@@ -93,6 +98,8 @@ export class EntityManager {
   }
 
   getNextId(): EntityId {
-    return Math.max(0, ...this.actors.keys()) + 1;
+    this.lastId++;
+    return this.lastId;
   }
 }
+