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How To Use Coverage in Django

When you are developing a large project it is usually to forget some parts of the code you want to tests. Coverage.py is a python tool that helps you to know that information.

Installation

Use pip or easy_install, as you want

pip install coverage 

Running and erasing

For running on a django project, use this command

coverage run --source='.' manage.py test the-app-you-want-to-test

This command will fill a “.coverage”, located in COVERAGE_FILE and then you may see results or report. If you need to remove gathered data, execute:

coverage erase

For a single file

Maybe you only want to check a python code, then do

coverage run your_program.py arg1 arg2 arg3

There are some additional options, take a look on https://coverage.readthedocs.io/en/coverage-4.3.4/cmd.html#execution

About templates, see the plugin section and install one of those eggs:

See results

If you want to show the results in the command line, run:

coverage report

For more readable reports:

coverage html

To know concretely what part of your code is covered by tests, use:

coverage annotate -d directory-where-to-put-annotated-files

It will generate same source code file with an additional syntax on it:

  • Line with “>” means it was executed

  • Line beginning with “!” means it was not executed

  • Line starting with “-” means the line was excluded in the coverage statistics

Good coverage level

A good coverage usually comes on 90%. However, if you see 100% it could be not so good signal because it could be someone dealing with coverage instead of quality of tests.

Some tips:

  • Be careful with the quality of your tests

  • Don’t slow down your dev. velocity of the sake of the coverage

  • Use coverage to find untested code and decide if it deserve to cover

Excluding code

So far so good, however sometimes we need to exclude some code that we don’t need to cover. There are several options:

  1. Specifying files to exclude and omit in .coveragerc

  2. Writing in the same line of a block the comment

 # pragma: no cover

For example, if you want to exclude generated code from coverage because it is suppossed to be maintained by the generation tool:

def generated_code():   # pragma: no cover
   do_something()

If you like this library, don’t miss more features and take a deep dive into Coverage.py documentation.

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