Javascript 如何为chai expect提供用于mocha单元测试的自定义错误消息？

我用chai's expect进行了摩卡咖啡测试：

it("should parse sails out of cache file", async () => {
    const sailExtractor = new Extractor();
    const result = await sailExtractor.extract("test.xml");

    try {
        expect(result.length).to.be.greaterThan(0);
        const withMandatoryFlight = result.filter((cruises) => {
            return cruises.hasMandatoryFlight === true;
        });
        expect(withMandatoryFlight.length).to.be.greaterThan(0);
        const cruiseOnly = result.filter((cruises) => {
            return cruises.hasMandatoryFlight === false;
        });

        expect(cruiseOnly.length).to.be.greaterThan(0);

        return Promise.resolve();
    } catch (e) {
        return Promise.reject(e);
    }
}

现在，如果一个

to.be.greaterThan（0）

预期失败，那么mocha上的错误输出对开发人员不友好：

 AssertionError: expected 0 to be above 0
      at Assertion.assertAbove (node_modules/chai/lib/chai/core/assertions.js:571:12)
      at Assertion.ctx.(anonymous function) [as greaterThan] (node_modules/chai/lib/chai/utils/addMethod.js:41:25)
      at _callee2$ (tests/unit/operator/croisiEurope/CroisXmlExtractorTest.js:409:61)
      at tryCatch (node_modules/regenerator-runtime/runtime.js:65:40)
      at Generator.invoke [as _invoke] (node_modules/regenerator-runtime/runtime.js:303:22)
      at Generator.prototype.(anonymous function) [as next] (node_modules/regenerator-runtime/runtime.js:117:21)
      at fulfilled (node_modules/tslib/tslib.js:93:62)
      at <anonymous>
      at process._tickDomainCallback (internal/process/next_tick.js:228:7)

然后失败的mocha错误应打印：

 AssertionError: It should parse at least one sail out of the flatfile, but result is empty

---

如果对断言使用

should

，则可以向测试函数传递一个字符串，如果条件失败，该字符串将被写出。例如：

result.length.should.be.above(0, "It should parse at least one sail out of the flatfile, but result is empty");

---

我不确定这在expect中是否可行。API似乎没有提到它。

每个

expect

方法都接受一个可选参数

消息

：

expect(1).to.be.above(2, 'nooo why fail??');
expect(1, 'nooo why fail??').to.be.above(2);

因此，在您的情况下，应该是：

expect(result.length)
  .to.be.greaterThan(0, "It should parse at least one sail out of the flatfile, but result is empty");

---

OP正在使用

chai

，但您的答案似乎也适用于该库。或者，您可以使用

expect（result.length，'It should parse…）.to.be.greaterThan（0）

Sidenote：由于我使用的是typescript，我可以通过跳入

greaterThan

方法找到它，因为它的类型声明为，并且显示了可选的消息参数。这对我不起作用，但是自定义消息是。我意识到这已经很旧了，但只是为了确认这在语法

myCollection.should.have.length（1，“oopsy”）中确实适用。奇怪的是@liminal18却没有。谢谢你的回答！
expect(result.length)
  .to.be.greaterThan(0, "It should parse at least one sail out of the flatfile, but result is empty");