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This plugin produces coverage reports. It supports centralised testing and distributed testing in both load and each modes. It also supports coverage of subprocesses.

All features offered by the coverage package should be available, either through pytest-cov or through coverage's config file.

• Free software: MIT license

Install with pip:

pip install pytest-cov

For distributed testing support install pytest-xdist:

pip install pytest-xdist

pytest-cov 2.0 is using a new .pth file (pytest-cov.pth). You may want to manually remove the older init_cov_core.pth from site-packages as it's not automatically removed.

Uninstall with pip:

pip uninstall pytest-cov

Under certain scenarios a stray .pth file may be left around in site-packages.

• pytest-cov 2.0 may leave a pytest-cov.pth if you installed without wheels (easy_install, setup.py install etc).
• pytest-cov 1.8 or older will leave a init_cov_core.pth.

Centralised testing will report on the combined coverage of the main process and all of its subprocesses.

Running centralised testing:

py.test --cov=myproj tests/

Shows a terminal report:

-------------------- coverage: platform linux2, python 2.6.4-final-0 ---------------------
Name                 Stmts   Miss  Cover
----------------------------------------
myproj/__init__          2      0   100%
myproj/myproj          257     13    94%
myproj/feature4286      94      7    92%
----------------------------------------
TOTAL                  353     20    94%

Distributed testing with dist mode set to load will report on the combined coverage of all slaves. The slaves may be spread out over any number of hosts and each slave may be located anywhere on the file system. Each slave will have its subprocesses measured.

Running distributed testing with dist mode set to load:

py.test --cov=myproj -n 2 tests/

Shows a terminal report:

-------------------- coverage: platform linux2, python 2.6.4-final-0 ---------------------
Name                 Stmts   Miss  Cover
----------------------------------------
myproj/__init__          2      0   100%
myproj/myproj          257     13    94%
myproj/feature4286      94      7    92%
----------------------------------------
TOTAL                  353     20    94%

Again but spread over different hosts and different directories:

py.test --cov=myproj --dist load
        --tx ssh=memedough@host1//chdir=testenv1
        --tx ssh=memedough@host2//chdir=/tmp/testenv2//python=/tmp/env1/bin/python
        --rsyncdir myproj --rsyncdir tests --rsync examples
        tests/

Shows a terminal report:

-------------------- coverage: platform linux2, python 2.6.4-final-0 ---------------------
Name                 Stmts   Miss  Cover
----------------------------------------
myproj/__init__          2      0   100%
myproj/myproj          257     13    94%
myproj/feature4286      94      7    92%
----------------------------------------
TOTAL                  353     20    94%

Distributed testing with dist mode set to each will report on the combined coverage of all slaves. Since each slave is running all tests this allows generating a combined coverage report for multiple environments.

Running distributed testing with dist mode set to each:

py.test --cov=myproj --dist each
        --tx popen//chdir=/tmp/testenv3//python=/usr/local/python27/bin/python
        --tx ssh=memedough@host2//chdir=/tmp/testenv4//python=/tmp/env2/bin/python
        --rsyncdir myproj --rsyncdir tests --rsync examples
        tests/

Shows a terminal report:

---------------------------------------- coverage ----------------------------------------
                          platform linux2, python 2.6.5-final-0
                          platform linux2, python 2.7.0-final-0
Name                 Stmts   Miss  Cover
----------------------------------------
myproj/__init__          2      0   100%
myproj/myproj          257     13    94%
myproj/feature4286      94      7    92%
----------------------------------------
TOTAL                  353     20    94%

It is possible to generate any combination of the reports for a single test run.

The available reports are terminal (with or without missing line numbers shown), HTML, XML and annotated source code.

The terminal report without line numbers (default):

py.test --cov-report term --cov=myproj tests/

-------------------- coverage: platform linux2, python 2.6.4-final-0 ---------------------
Name                 Stmts   Miss  Cover
----------------------------------------
myproj/__init__          2      0   100%
myproj/myproj          257     13    94%
myproj/feature4286      94      7    92%
----------------------------------------
TOTAL                  353     20    94%

The terminal report with line numbers:

py.test --cov-report term-missing --cov=myproj tests/

-------------------- coverage: platform linux2, python 2.6.4-final-0 ---------------------
Name                 Stmts   Miss  Cover   Missing
--------------------------------------------------
myproj/__init__          2      0   100%
myproj/myproj          257     13    94%   24-26, 99, 149, 233-236, 297-298, 369-370
myproj/feature4286      94      7    92%   183-188, 197
--------------------------------------------------
TOTAL                  353     20    94%

The terminal report with skip covered:

py.test --cov-report term:skip-covered --cov=myproj tests/

-------------------- coverage: platform linux2, python 2.6.4-final-0 ---------------------
Name                 Stmts   Miss  Cover
----------------------------------------
myproj/myproj          257     13    94%
myproj/feature4286      94      7    92%
----------------------------------------
TOTAL                  353     20    94%

1 files skipped due to complete coverage.

You can use skip-covered with term-missing as well. e.g. --cov-report term-missing:skip-covered

These three report options output to files without showing anything on the terminal:

py.test --cov-report html
        --cov-report xml
        --cov-report annotate
        --cov=myproj tests/

The output location for each of these reports can be specified. The output location for the XML report is a file. Where as the output location for the HTML and annotated source code reports are directories:

py.test --cov-report html:cov_html
        --cov-report xml:cov.xml
        --cov-report annotate:cov_annotate
        --cov=myproj tests/

The final report option can also suppress printing to the terminal:

py.test --cov-report= --cov=myproj tests/

This mode can be especially useful on continuous integration servers, where a coverage file is needed for subsequent processing, but no local report needs to be viewed. For example, tests run on Travis-CI could produce a .coverage file for use with Coveralls.

The data file is erased at the beginning of testing to ensure clean data for each test run. If you need to combine the coverage of several test runs you can use the --cov-append option to append this coverage data to coverage data from previous test runs.

The data file is left at the end of testing so that it is possible to use normal coverage tools to examine it.

This plugin provides a clean minimal set of command line options that are added to pytest. For further control of coverage use a coverage config file.

For example if tests are contained within the directory tree being measured the tests may be excluded if desired by using a .coveragerc file with the omit option set:

py.test --cov-config .coveragerc
        --cov=myproj
        myproj/tests/

Where the .coveragerc file contains file globs:

[run]
omit = tests/*

For full details refer to the coverage config file documentation.

Note that this plugin controls some options and setting the option in the config file will have no effect. These include specifying source to be measured (source option) and all data file handling (data_file and parallel options).

For distributed testing the slaves must have the pytest-cov package installed. This is needed since the plugin must be registered through setuptools for pytest to start the plugin on the slave.

For subprocess measurement environment variables must make it from the main process to the subprocess. The python used by the subprocess must have pytest-cov installed. The subprocess must do normal site initialisation so that the environment variables can be detected and coverage started.

When it comes to TDD one obviously would like to debug tests. Debuggers in Python use mostly the sys.settrace function to gain access to context. Coverage uses the same technique to get access to the lines executed. Coverage does not play well with other tracers simultaneously running. This manifests itself in behaviour that PyCharm might not hit a breakpoint no matter what the user does. Since it is common practice to have coverage configuration in the pytest.ini file and pytest does not support removeopts or similar the --no-cov flag can disable coverage completely.

At the reporting part a warning message will show on screen

Coverage disabled via --no-cov switch!

Whilst this plugin has been built fresh from the ground up it has been influenced by the work done on pytest-coverage (Ross Lawley, James Mills, Holger Krekel) and nose-cover (Jason Pellerin) which are other coverage plugins.

Ned Batchelder for coverage and its ability to combine the coverage results of parallel runs.

Holger Krekel for pytest with its distributed testing support.

Jason Pellerin for nose.

Michael Foord for unittest2.

No doubt others have contributed to these tools as well.