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

Question

我有一个使用 chai 的期望的 mocha 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) 期望失败，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)

我想用更人性化的东西来代替它。有没有办法告诉 chai 使用自定义错误消息？

我希望能够像这个伪代码一样使用它：

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

然后应该打印失败的摩卡错误：

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

Answer 1

如果您将should 用于您的断言，您可以将一个字符串传递给测试函数，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");

我不确定这是否可以通过expect 实现。 API 似乎没有提及它。

Answer 2

每个expect 方法都接受一个可选参数message：

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

所以，在你的情况下应该是：

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