Outreachy: The learning phase

We are happy that Open Humans will have four Outreachy interns this summer. Our interns are working on their own Open Humans related projects and will regularly blog about their internship experience. Read Tarannum’s post about working on creating packages  for the Open Humans API:

The Open Humans API provides command line tools to interact with Open Humans. From where, I started working with Open Humans API to where it is now, the transformation has been just magical.

With the help of Open Humans organisation mentors,  lot of features were added like messaging and uploading large files with the help of AWS. From learning the proper way to name the functions to testing the functions, documenting the API using Sphinx, adding more command line tools, every smaller piece of learning added to create an avalanche of wisdom.

For legacy code, test is a necessity. The code is full of logic, it’s alive and it’s core to any application. We need to keep going back to the code to update it, so tests are crucial.

I mocked the API test using VCR.py . It’s just like Thor’s stormbreaker (Marvel fan will understand) in the field of unit testing. It’s apt for those applications which make http calls to external services(in my case Open Humans).

Why VCR.py

The external service should not be tightly coupled with the application. If the external services fail, the application should still run correctly. One absolute novice testing way is to hard code error prone request and code the necessary error handling routines. But, this is highly not recommended because once you update even a few line of code, you have to manually test it again. So, we hop on to the more sophisticated way of testing: Unittesting.

Running tests which call the external service every time will be very slow. Apart from it, the tests won’t work offline and sending too many requests to the external service can be a problem too. So, here steps the protagonist, VCR.py. 🙂

You just need to run the test online once when the cassette file which stores all the important information related to the requests response has not been created. Once, it is done, the response of requests will just be compared with the cassette file and yes , it’s done 🙂 . You have became successful in making your application more sturdy.

How to use VCR.py

For each function serving a particular feature, a class for testing is created. For testing different lines of code of a particular feature, different tests(functions with assertion) is created in the test class. Tests for valid response, invalid responses are written.

For the first time, when the test is run, the request really hits the external service and a cassette file is formed. Once the cassette is formed which contain status codes, status, etc, the response of tests is just compared with the cassette file when the tests are run again. It really speeds up the testing process and saves us from sending requests to the external service again and again. Whether you are offline at your home or 40,000 feet above the ground anytime you can test your code, once the cassettes are formed.

Want to try a hand on this cool stuff?  You can follow this https://github.com/OpenHumans/open-humans-api/blob/master/ohapi/tests/test_api.py. The link contains a lot of examples to write tests using vcr.py. You can see the bigger picture by observing any function in the https://github.com/OpenHumans/open-humans-api/blob/master/ohapi/api.py and how for each functions tests and cassettes are formed.

I would like to thank Mad Price Ball for mentoring me in the best way possible. The meetings with them are fun where I learn a lot of new stuff and a new way to see things, to tackle an issue with a fresh perspective.

Apart from this, I also worked on testing the public functions of Open Humans API. Presently, I am working on creating a reusable django app for Open Humans. A lot of brainstorming goes while you are in the process of designing an application, it’s use cases, what kind of audience it will cater.

Reusable application are the application which will be used by other applications. After all, reusability is the way of life in Python. I will cover the reusable app topic in my next blog. Till then, stay tuned. 🙂

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