Smoke testing Swagger-based Web Services

Swagger has come a long way. The project got renamed ("Open API") and it seems to have a vibrant community.

If you are not familiar with it, it's a specification to describe your HTTP endpoints (spec here) that has been around since a few years now ~ and it seems to be getting really mature at this point.

I was surprised to find out how many available tools they are now. The dedicated page has a serious lists of tools.

There's even a Flask-based framework used by Zalando to build microservices.

Using Swagger makes a lot of sense for improving the discoverability and documentation of JSON web services. But in my experience, with these kind of specs it's always the same issue: unless it provides a real advantage for developers, they are not maintained and eventually removed from projects.

So that's what I am experimenting on right now.

One use case that interests me the most is to see whether we can automate part of the testing we're doing at Mozilla on our web services by using Swagger specs.

That's why I've started to introduce Swagger on a handful of projects, so we can experiment on tools around that spec.

One project I am experimenting on is called Smwogger, a silly contraction of Swagger and Smoke (I am a specialist of stupid project names.)

The plan is to see if we can fully automate smoke tests against our APIs. That is, a very simple test scenario against a deployment, to make sure everything looks OK.

In order to do this, I have added an extension to the spec, called x-smoke-test, where developers can describe a simple scenario to test the API with a couple of assertions. There are a couple of tools like that already, but I wanted to see whether we could have one that could be 100% based on the spec file and not require any extra coding.

Since every endpoint has an operation identifier, it's easy enough to describe it and have a script (==Smwogger) that plays it.

Here's my first shot at it... The project is at https://github.com/tarekziade/smwogger and below is an extract from its README

Running Smwogger

To add a smoke test for you API, add an x-smoke-test section in your YAML or JSON file, describing your smoke test scenario.

Then, you can run the test by pointing the Swagger spec URL (or path to a file):

$ bin/smwogger smwogger/tests/shavar.yaml
Scanning spec... OK

        This is project 'Shavar Service'
        Mozilla's implementation of the Safe Browsing protocol
        Version 0.7.0


Running Scenario
1:getHeartbeat... OK
2:getDownloads... OK
3:getDownloads... OK

If you need to get details about the requests and responses sent, you can use the -v option:

$ bin/smwogger -v smwogger/tests/shavar.yaml
Scanning spec... OK

        This is project 'Shavar Service'
        Mozilla's implementation of the Safe Browsing protocol
        Version 0.7.0


Running Scenario
1:getHeartbeat...
GET https://shavar.somwehere.com/__heartbeat__
>>>
HTTP/1.1 200 OK
Content-Type: text/plain; charset=UTF-8
Date: Mon, 21 Nov 2016 14:03:19 GMT
Content-Length: 2
Connection: keep-alive

OK
<<<
OK
2:getDownloads...
POST https://shavar.somwehere.com/downloads
Content-Length: 30

moztestpub-track-digest256;a:1

>>>
HTTP/1.1 200 OK
Content-Type: application/octet-stream
Date: Mon, 21 Nov 2016 14:03:23 GMT
Content-Length: 118
Connection: keep-alive

n:3600
i:moztestpub-track-digest256
ad:1
u:tracking-protection.somwehere.com/moztestpub-track-digest256/1469223014

<<<
OK
3:getDownloads...
POST https://shavar.somwehere.com/downloads
Content-Length: 35

moztestpub-trackwhite-digest256;a:1

>>>
HTTP/1.1 200 OK
Content-Type: application/octet-stream
Date: Mon, 21 Nov 2016 14:03:23 GMT
Content-Length: 128
Connection: keep-alive

n:3600
i:moztestpub-trackwhite-digest256
ad:1
u:tracking-protection.somwehere.com/moztestpub-trackwhite-digest256/1469551567

<<<
OK

Scenario

A scenario is described by providing a sequence of operations to perform, given their operationId.

For each operation, you can make some assertions on the response by providing values for the status code and some headers.

Example in YAML

x-smoke-test:
  scenario:
  - getSomething:
      response:
        status: 200
        headers:
          Content-Type: application/json
  - getSomethingElse
      response:
        status: 200
  - getSomething
      response:
        status: 200

If a response does not match, an assertion error will be raised.

Posting data

When you are posting data, you can provide the request body content in the operation under the request key.

Example in YAML

x-smoke-test:
  scenario:
  - postSomething:
      request:
        body: This is the body I am sending.
      response:
        status: 200

Replacing Path variables

If some of your paths are using template variables, as defined by the swagger spec, you can use the path option:

x-smoke-test:
  scenario:
  - postSomething:
      request:
        body: This is the body I am sending.
        path:
          var1: ok
          var2: blah
      response:
        status: 200

You can also define global path values that will be looked up when formatting paths. In that case, variables have to be defined in a top-level path section:

x-smoke-test:
  path:
    var1: ok
  scenario:
  - postSomething:
      request:
        body: This is the body I am sending.
        path:
          var2: blah
      response:
        status: 200

Variables

You can extract values from responses, in order to reuse them in subsequential operations, wether it's to replace variables in path templates, or create a body.

For example, if getSomething returns a JSON dict with a "foo" value, you can extract it by declaring it in a vars section inside the response key:

x-smoke-test:
  path:
    var1: ok
  scenario:
  - getSomething:
      request:
        body: This is the body I am sending.
        path:
          var2: blah
      response:
        status: 200
        vars:
          foo:
            query: foo
            default: baz

Smwogger will use the query value to know where to look in the response body and extract the value. If the value is not found and default is provided, the variable will take that value.

Once the variable is set, it will be reused by Smwogger for subsequent operations, to replace variables in path templates.

The path formatting is done automatically. Smwogger will look first at variables defined in operations, then at the path sections.

Conclusion

None for now. This is an ongoing experiment. But happy to get your feedback on github!

Comments !