如何使用sinon.js存根https.request response.pipe？

Question

假设我有以下简单代码：

var https = require('https');
var options = {
  host: 'openshift.redhat.com',
  port: 443,
  path: '/broker/rest/api',
  method: 'GET'
};
var req = https.request(options, function(response) {
  console.log(response.statusCode);
  response.pipe(save stream to file with fs)
});
req.on('error', function(e) {
  console.error(e);
});
req.end();

好吧，我对sinon.js有点陌生，我想问一下：如何存入response.pipe（）？当然，我可以对https.request进行存根处理并使用.on和.end返回某物很简单，但是我不知道如何测试response.pipe（）是否使用适当的参数...（nodejs文档）说响应是回调），在这种情况下，文档无济于事！ofc testing env是mocha，也可以使用chai，请给我一些建议或示例。谢谢，马特

Answer 1

我将您的代码包装到一个接受回调的函数中，因为在当前实现中，我们实际上并不知道管道何时实际完成。因此，假设我们具有如下功能：

const downloadToFile = function (options, callback) {
	let req = https.request(options, function (err, stream) {
		let writeStream = fs.createWriteStream('./output.json');
		stream.pipe(writeStream);

		//Notify that the content was successfully writtent into a file
		stream.on('end', () => callback(null));
		//Notify the caller that error happened.
		stream.on('error', err => callback(err));
	});

	req.end();
};

有3个问题需要解决：

1. 响应是可读流。我们想模拟它发出的数据。
2. 我们想模拟.pipe方法检查是否将管道传递到正确的流。
3. 我们还需要模拟https.request方法而不进行实际调用

这是我们可以实现的方法：

const {PassThrough} = require('stream');

describe('#downloadToFile', () => {
	it('should save the data to output.json', function (callback) {
		const mockResponse = `{"data": 123}`;
		//Using a built-in PassThrough stream to emit needed data.
		const mockStream = new PassThrough();
		mockStream.push(mockResponse);
		mockStream.end(); //Mark that we pushed all the data.

		//Patch the 'https' module not to make an actual call
		//but to return our stream instead
		sinon.stub(https, 'request', function (options, callback) {
			callback(null, mockStream);

			return {end: sinon.stub()}; //Stub end method btw
		});

		//Finally keep track of how 'pipe' is going to be called
		sinon.spy(mockStream, 'pipe');

		downloadToFile({url: 'http://google.com'}, (err) => {
			//Here you have the full control over what's happened
			sinon.assert.calledOnce(mockStream.pipe);
			//We can get the stream that we piped to.
			let writable = mockStream.pipe.getCall(0).args[0];
			assert.equal(writable.path, './output.json');

			//Tell mocha that the test is finished. Pass an error if any.
			callback(err);
		});
	});
});

稍后，您可以创建单独的函数，例如：createMockedStream。甚至将所有这些准备工作提取到单独的方法中，并仅在测试中保留断言。