let fulfil; let thePromise = new Promise(f => { fulfil = f; }); export default { data: { thePromise }, html: ` <p>loading...</p> `, test(assert, component, target) { fulfil(42); return thePromise .then(() => { assert.htmlEqual(target.innerHTML, ` <p>the value is 42</p> `); let reject; thePromise = new Promise((f, r) => { reject = r; }); component.set({ thePromise }); assert.htmlEqual(target.innerHTML, ` <p>loading...</p> `); reject(new Error('something broke')); return thePromise.catch(() => {}); }) .then(() => { assert.htmlEqual(target.innerHTML, ` <p>oh no! something broke</p> `); }); } };