A mock implementation of XMLHttpRequest for unit testing
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This JavaScript module provides a mock implementation of XMLHttpRequest for unit testing. In nearly all ways it behaves like a regular XMLHttpRequest (with support for Progress Events), except of course it doesn't open a network connection. Instead it exposes the relevant data through the following extra attributes and methods:

method, url, async, user, password
These attributes correspond to the arguments of the open() method.
Object representing individual parts of the URL passed to open(), e.g. protocol, host, port, path, query, anchor. If present, the query string (query) is parsed and its elements are available from the queryKey property.
This attribute will contain the request body that was passed to the send() method.
Returns a request header set by the client.
setResponseHeader(header, value)
Sets a response header. This should be called before calling the receive() method.
receive(status, data)
Send data back to the client. status is an integer representing the HTTP status code (e.g. 200) and data is the response body (string).
Simulate a request error, such as NETWORK_ERR.
authenticate(user, password)
Verify HTTP credentials passed to open(), inserted into the URL, or sent via the Authorization header (in that order).

Simple example

Let's look at a brief example. Imagine you have this piece of code that wants to make an AJAX connection:

$ var request = new MockHttpRequest();
$ request.open("POST", "http://some.host/path");
$ request.setRequestHeader("Content-Type", "application/robot");
$ request.onload = function () {
>     print("Received response: " + this.statusText);
>     print("Response body: " + this.responseText);
> };
$ request.send("Hey meatbag!");

The request data will be set accordingly:

$ request.method
$ request.url
$ request.async

$ request.requestText
"Hey meatbag!"
$ request.getRequestHeader("Content-Type")

We can now simulate sending data back to the client:

$ request.receive(404, "Sorry, I have no idea what you're talking about.");
Received response: 404 Not Found
Response body: Sorry, I have no idea what you're talking about.

MockHttpServer for tests

Often you can't just change the client code to use MockHttpRequest for tests. In such cases, you can use MockHttpServer to intercept all instances of XMLHttpRequest.

For example, imagine you were trying to test a function called makeAJAXCall() that relied on getting information through XMLHttpRequest. First let's set up a server instance and define a request handler in which we mimick the server application and return whatever data the server would normally return:

var server = new MockHttpServer();
server.handle = function (request) {
    request.setResponseHeader("Content-Type", "application/robot");
    request.receive(200, "I am Bender, please insert girder!");

Now we can switch on the "server" to divert all XMLHttpRequests to our handler. Then we call the function we want to test. Finally we must not forget to clean up by stopping the server:



MockHttpRequest was written by Philipp von Weitershausen. It is released under the MIT License.