如何为摩卡unit testing提供自定义错误消息的chai expect？

我有一个使用柴的期望的摩卡testing：

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，摩卡上的错误输出不友好：

  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。 有没有办法告诉柴使用自定义错误消息？

我想能够像这样的伪代码使用它：

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

然后失败的摩卡错误应该打印：

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

Answer 1

每个expect方法接受一个可选的参数message ：

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

所以，你的情况应该是：

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

Answer 2

如果你用你的断言，你可以传递一个string到testing函数，如果条件失败将被写出来。 例如：

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

我不确定这是否可能与预期。 API似乎没有提到它。