如何在解析Promise时运行qunit断言

Question

我正在为一个返回promise的函数编写测试,并且无法在解析或拒绝promise时运行断言.我不能在这个项目上使用ES6所以我使用的是声称实现Promises/A +规范的rsvp.js库.我正在使用最新的qunit版本1.17.1

被测功能:

var loadGroups = function(data) {
     return new RSVP.Promise(function(resolve, reject) {
        var groups = [];
        // ... some code to populate the groups array
        if(groups.length > 0) {
            resolve(groups);
        } else {
            reject("No groups were loaded");
        }
    });
};

---

成功测试:

test('success test', function(assert) {
    assert.expect(1);

    var promise = loadGroups(testData);

    promise.then(function(groups) {
        assert.deepEquals(groups.length, 1);
    });

    return promise;
});

这失败了"预期的1个断言,但是0运行"

---

失败测试:

test('failure test', function(assert) {
    assert.expect(1);

    var promise = loadGroups([]);

    promise.then(null, function(message) {
        assert.equals(message, "No groups were loaded");
    });

    return promise;
});

这失败了"在加载空组时获得承诺时拒绝承诺:没有加载任何组"

Answer 1

承诺通过链接工作.Promise是值不可变的包装器.

当你这样做时:

promise.then(function(e){
   // do something
});

你并没有改变promise你正在创造一个新的承诺.相反,你需要链接承诺:

test('success test', function(assert) {
    assert.expect(1);

    var promise = loadGroups(testData);

    // return the `then` and not the original promise.
    return promise.then(function(groups) {
        assert.deepEquals(groups.length, 1);
    });

});