Create Tutorial - How to write backend unit tests.

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Skills covered

Python, Writing unit tests to cover all the known corner cases, Running unit tests.

Similar issues

Existing relevant pages

https://github.com/oppia/oppia/wiki/Backend-tests

Example

Write a git patch file to remove some of the existing tests of profile_test file.

Scenario: You have just written code for a profile_test file and now you need to write unit tests to cover your code. Understand the code first, try to think of general cases and then corner cases. Make sure it follows best practices and test it by running them in your local machine.