Things that will ruin your day when tests make HTTP requests to other services:
- That other service has the uptime of Twitter’s API
- Network late ………… ncy
- Being-rate limited and having to wait an hour for the next test run
- Same request returns different result each time
- Everyone else on the network is deep in BitTorrent terittory
Things node-replay can do to make these problems go away:
- Record API response once, replay as often as necessary
- Stub HTTP requests (TBD)
- Replay different responses to same request (great for testing error handling)
- Not suck
How to use node-replay
Like this:
Now write some simple test case:
assert = require("assert")
http = require("http")
replay = require("replay")
http.get({ hostname: "www.iheartquotes.com", path: "/api/v1/random" }, function(response) {
response.body = "";
response.on("data", function(chunk) {
response.body = response.body + chunk;
})
response.on("end", function() {
// Now check the request we made to the I <3 Quotes API
assert.equal(response.statusCode, 200);
assert.equal(response.body, "Oxymoron 2. Exact estimate\n\n[codehappy] http://iheartquotes.com/fortune/show/38021\n");
console.log("Woot!");
})
})This, of course, will fail the first time you run it. You’ll see:
Error: Connection to http://www.iheartquotes.com:80/api/v1/random refused: not recording and no network access
at Array.0 (/Users/assaf/projects/node-replay/lib/replay/proxy.coffee:87:21)
at EventEmitter._tickCallback (node.js:192:40)
Unless you tell it otherwise, node-replay runs in replay mode. In this mode it will replay any previously captured HTTP response, but it will not allow any outgoing network connection.
That’s the default mode for running tests. “Why?” you ask. Good question. Running in replay mode forces any test you run to use recorded reponses, and so it will run (and fail or pass) the same way for anyone else, any other day of the week, on whatever hardware they use. Even if they’re on the AT&T network.
Running in replay mode helps you write repeatable tests. Repeatable tests are a Good Thing.
So the first thing you want to do to get that test to pass, is to run node-replay in record mode. In this mode it will replay any recorded response, but if no response was recorded, it will make a request to the server and capture the response.
Let’s do that:
$ REPLAY=record node test.js
That wasn’t too hard, but the test is still failing. “How?” you must be wondering and scratching your head in total disbelief. It’s actually quite simple.
Every request you make to ‘I 3> Quotes’ returns a different quote, and that test is looking for a very specific quote. So the test will fail, and each time fail with a different error.
So one way we can fix this test is to change the assertion. Look at the error message, get the actual quote and make the assertion look for that value.
Now run the test:
Did the test pass? Of course it did. Run it again. Still passing? Why, yes.
So let’s have a look at that captured response. All the respones recorded for ‘I ‘ will be listed here:
$ ls fixtures/www.iheartquotes.com/
There should be only one file there, since we only recorded one response. The file name is a timestamp, but feel free to rename it to something more rescriptive.
The name of a response file doesn’t matter, it can be whatever you want. The name of the directory does, though, it matches the service hostname (and port when not 80).
So that was one way to fix the failing test. Another one is to change the recorded response to match the assertion. Being able to edit (and create new) responses is quite important. Sometimes it’s the easiest way to create mock responses for testing, e.g. if you’re trying to test failure conditions that are hard to come by.
So let’s edit the response file and change the body part, so the entire response reads like this:
/api/v1/random
200 HTTP/1.1
server: nginx/0.7.67
date: Fri, 02 Dec 2011 02:58:03 GMT
content-type: text/plain
etag: "a7131ebc1e81e43ea9ecf36fa2fdf610"
cache-control: max-age=0, private, must-revalidate
Oxymoron 2. Exact estimate
[codehappy] http://iheartquotes.com/fortune/show/38021
All responses are stored as text files using the simplest format ever, so you can edit them in Vim, or any of the many non-Vim text editors in existence:
- First comes the request path (including query string)
- Followed by any headers sent as part of the request (like
Accept and Authorization)
- Then an empty line
- Next the response status code and (optional) HTTP version number
- Followed by any headers sent as part of the response
- Then another empty line
- And the rest taken by the response body
Settings
We’ve got them. Just enough to make you happy and not enough to take all day to explain.
The first and most obvious is the mode you run node-reply in:
bloody – All requests go out, none get replayed. Use this if you want to remember what life was before you started using node-replay. Also, to test your code against changes to 3rd party API, because these do happen. Too often.
cheat – Replays recorded responses, and allow HTTP outbound requests. This is mighty convenient when you’re writing new tests or changing code to make new, un-recorded HTTP requests, but you haven’t quite settled on which requets to make, so you don’t want any responses recorded quite yet.
record – Replays recorded responses, or captures responses for future replay. Use this whenever you’re writing new tests or code that makes new HTTP requests.
replay – Replays recorded responses, does not allow outbound requests. This is the default node. That’s another way of saying, “you’ll be running in this mode most of the time”.
Of course, node-reply needs to store all those captured responses somewhere, and by default it will put them in the directory fixtures. Bet you have an idea for a better directory name. Easy to change.
Like this:
var replay = require("replay");
replay.fixtures = __dirname + "/fixtures/replay"If you’re running into trouble, try turning debugging mode on. It helps. Sometimes.
$ DEBUG=true node test.js
Requesting http://www.iheartquotes.com:80/api/v1/random
Woot!
Geeking
To make all that magic possible, node-replay replaces require('http').request with its own method. That method returns a ProxyRequest object that captures the request URL, headers and body.
When it’s time to fire the request, it gets sent through a chain of proxies. The first proxy to have a response, returns it (via callback, this is Node.js after all). That terminates the chain. A proxy that doesn’t have a response still has to call the callback, but with no arguments. The request will then pass to the next proxy down the chain.
The proxy chain looks something like this:
- Logger dumps the request URL when running with
DEBUG=true
- The pass-through proxy will pass the request directly to the server in
bloody mode, or when talking to localhost
- The recorder proxy will either replay a captured request (if it has one), talk to the server and capture the response (in
record mode), or pass to the next proxy
- The pass-through proxy (2nd one) will pass the request to the server in
cheat mode, return nothing in all other modes
Loading pre-recorded responses to memory, from where they can be replayed, and storing new ones on disk, is handled by … cue big band … theCatalog.
Enjoy.
