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Mocking SMTP when testing a black box of software

So I wrote a micro service that gets a REST call and sends a mail or a SMS and I wanted to have some nice black box tests in place.

The test

So my test would POST to a web service, then wait for a little while and then check if a mail was sent. The test runs remotely from a build server so everything it needs needs to be accesible over HTTP. So I decided to have a real SMTP server running on the server writing files to a directory that a web server can pick up and show to the test. And a static web server serving the mail files in that directory. Pseudo code:

random_id = UUID.generate()
message = subject: random_id, message: 'long rant'
server.post message
wait 1000
list_of_mails = staticServer.get
assert list_of_mails =~ random_ud

Dummy SMTP server

I looked around on the Internet for a while. I used a Java based graphical dummy server locally called FakeSMTP. It is really useful when doing stuff in a graphical environment. Now I needed something headless instead. My eyes fell on a small Python script that did almost exactly what I wanted. The only thing missing was the naming of the files. In order to trace a mail through the server onto the SMTP server I needed something unique. I decided to put a UUID as the subject. The Python script needed a little tweak to get the subject (as well as the timestamp) onto the filename.

The script only works with Python 2 so make sure you have it….. I am sure it is easy to change for Python 3 for a pythonista.

Simple file serving web server

Since the system under test lives in a tomcat I started out trying to make tomcat serve static files from the folder where the SMTP server stuffs mail files. It is supposed to work but I had some problems and gave up deciding to search for a simpler solution. And suddenly there it was. Look at this beauty:

python -m SimpleHTTPServer

Get yourself into a directory from where you want to serve static files - type the above into the terminal and you are up and running on port 8000.

Closing rant about naming

Integration tests can mean many things. There seem to be no common vocabulary within the testing discipline. In Grails - the framework used in the micro service here - integration testing means talking directly to a controller and stubbing away third party dependencies. So the meaning here is to test the different parts and of a system together. (As opposite to unit testing.) For me integration testing normally means testing a couple of systems together and accessing it from the outside (normally with HTTP in some form). This confusion about names led me to use black box testing in this article. Using another name for this does not really help but when talking about black boxes it is obvious that we are not testing or knows about any internals - a good thing.

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