implement basic assert in cucumber world

test/core/001.feature

@@ -2,4 +2,4 @@ Feature:
 
 Scenario:
   Given I start playing
-  Then I will have fun
+  Then the current turn is 1

test/steps.js

@@ -1,10 +1,10 @@
-import {Given, When} from '@cucumber/cucumber';
+import {Given, Then} from '@cucumber/cucumber';
 
 Given('I start playing', function () {
-
+  this.start();
 });
 
-When('I will have fun', function () {
-
+Then('the current turn is {int}', async function (expected_turn) {
+  await this.assert(({turn}) => turn === expected_turn);
 });
 

test/world.js

@@ -1,10 +1,20 @@
 import {World, setWorldConstructor} from '@cucumber/cucumber';
+import {waitFor} from 'xstate';
+import game from '../src/game.js';
 
 setWorldConstructor(class extends World {
 
   constructor(options) {
     super(options);
   }
 
+  start() {
+    this.game = game();
+    this.game.start();
+  }
+
+  async assert(predicate) {
+    await waitFor(this.game, ({context}) => predicate(context), {timeout: 2000});
+  }
 });