diff-cover

diff-cover, pypi-version, conda-version, build-status, coverage-status, docs-status, ========================================================================================

Automatically find diff lines that need test coverage.
Also finds diff lines that have violations (according to tools such
as pycodestyle, pyflakes, flake8, or pylint).
This is used as a code quality metric during code reviews.

Overview

Diff coverage is the percentage of new or modified
lines that are covered by tests. This provides a clear
and achievable standard for code review: If you touch a line
of code, that line should be covered. Code coverage
is every developer's responsibility!

The diff-cover command line tool compares an XML coverage report
with the output of git diff. It then reports coverage information
for lines in the diff.

Currently, diff-cover requires that:

• You are using git for version control.
• Your test runner generates coverage reports in Cobertura, Clover
  or JaCoCo XML format.

Supported XML coverage reports can be generated with many coverage tools,
including:

• Cobertura__ (Java)
• Clover__ (Java)
• JaCoCo__ (Java)
• coverage.py__ (Python)
• JSCover__ (JavaScript)

__ http://cobertura.sourceforge.net/
__ http://openclover.org/
__ https://www.jacoco.org/
__ http://nedbatchelder.com/code/coverage/
__ http://tntim96.github.io/JSCover/

diff-cover is designed to be extended. If you are interested
in adding support for other version control systems or coverage
report formats, see below for information on how to contribute!

Installation

To install the latest release:

.. code:: bash

pip install diff_cover

To install the development version:

.. code:: bash

git clone https://github.com/Bachmann1234/diff-cover.git
cd diff-cover
python setup.py install

Getting Started

1. Set the current working directory to a git repository.

2. Run your test suite under coverage and generate a [Cobertura, Clover or JaCoCo] XML report.
   For example, using pytest-cov__:

.. code:: bash

pytest --cov --cov-report=xml

__ https://pypi.org/project/pytest-cov

This will create a coverage.xml file in the current working directory.

NOTE: If you are using a different coverage generator, you will
need to use different commands to generate the coverage XML report.

3. Run diff-cover:

.. code:: bash

diff-cover coverage.xml

This will compare the current git branch to origin/master and print
the diff coverage report to the console.

You can also generate an HTML version of the report:

.. code:: bash

diff-cover coverage.xml --html-report report.html

Multiple XML Coverage Reports

In the case that one has multiple xml reports form multiple test suites, you
can get a combined coverage report (a line is counted as covered if it is
covered in ANY of the xml reports) by running diff-cover with multiple
coverage reports as arguments. You may specify any arbitrary number of coverage
reports:

.. code:: bash

diff-cover coverage1.xml coverage2.xml

Quality Coverage

You can use diff-cover to see quality reports on the diff as well by running
diff-quality.

.. code :: bash

diff-quality --violations=<tool>

Where tool is the quality checker to use. Currently pycodestyle, pyflakes,
flake8, pylint, checkstyle, checkstylexml are supported, but more
checkers can (and should!) be supported. See the section "Adding `diff-quality``
Support for a New Quality Checker".

NOTE: There's no way to run findbugs from diff-quality as it operating
over the generated java bytecode and should be integrated into the build
framework.

Like diff-cover, HTML reports can be generated with

.. code:: bash

diff-quality --violations=<tool> --html-report report.html

If you have already generated a report using pycodestyle, pyflakes, flake8,
pylint, checkstyle, checkstylexml, or findbugs you can pass the report
to diff-quality. This is more efficient than letting diff-quality re-run
pycodestyle, pyflakes, flake8, pylint, checkstyle, or checkstylexml.

.. code:: bash

# For pylint < 1.0
pylint -f parseable > pylint_report.txt

# For pylint >= 1.0
pylint --msg-template="{path}:{line}: [{msg_id}({symbol}), {obj}] {msg}" > pylint_report.txt

# Use the generated pylint report when running diff-quality
diff-quality --violations=pylint pylint_report.txt

# Use a generated pycodestyle report when running diff-quality.
pycodestyle > pycodestyle_report.txt
diff-quality --violations=pycodestyle pycodestyle_report.txt

Note that you must use the -f parseable option to generate
the pylint report for pylint versions less than 1.0 and the
--msg-template option for versions >= 1.0.

diff-quality will also accept multiple pycodestyle, pyflakes, flake8,
or pylint reports:

.. code:: bash

diff-quality --violations=pylint report_1.txt report_2.txt

If you need to pass in additional options you can with the options flag

.. code:: bash

diff-quality --violations=pycodestyle --options="--exclude='*/migrations*' --statistics" pycodestyle_report.txt

Compare Branch

By default, diff-cover compares the current branch to origin/master. To specify a different compare branch:

.. code:: bash

diff-cover coverage.xml --compare-branch=origin/release

Fail Under

To have diff-cover and diff-quality return a non zero status code if the report quality/coverage percentage is
below a certain threshold specify the fail-under parameter

.. code:: bash

diff-cover coverage.xml --fail-under=80
diff-quality --violations=pycodestyle --fail-under=80

The above will return a non zero status if the coverage or quality score was below 80%.

Troubleshooting

Issue: diff-cover always reports: "No lines with coverage information in this diff."

Solution: diff-cover matches source files in the coverage XML report with
source files in the git diff. For this reason, it's important
that the relative paths to the files match. If you are using coverage.py__
to generate the coverage XML report, then make sure you run
diff-cover from the same working directory.

__ http://nedbatchelder.com/code/coverage/

Issue: GitDiffTool._execute() raises the error:

.. code:: bash

fatal: ambiguous argument 'origin/master...HEAD': unknown revision or path not in the working tree.

This is known to occur when running diff-cover in Travis CI__

__ http://travis-ci.org

Solution: Fetch the remote master branch before running diff-cover:

.. code:: bash

git fetch origin master:refs/remotes/origin/master

Issue: diff-quality reports "diff_cover.violations_reporter.QualityReporterError: No config file found, using default configuration"

Solution: Your project needs a pylintrc file. Provide this file (it can be empty) and diff-quality should run without issue.

Issue: diff-quality reports "Quality tool not installed"

Solution: diff-quality assumes you have the tool you wish to run against your diff installed. If you do not have it
then install it with your favorite package manager.

License

The code in this repository is licensed under the Apache 2.0 license.
Please see LICENSE.txt for details.

How to Contribute

Contributions are very welcome. The easiest way is to fork this repo, and then
make a pull request from your fork. The first time you make a pull request, you
may be asked to sign a Contributor Agreement.

NOTE: diff-quality supports a plugin model, so new tools can be integrated
without requiring changes to this repo. See the section "Adding `diff-quality``
Support for a New Quality Checker".

Setting Up For Development

diff-cover is written to support many versions of Python. The best way to set
your machine up for development is to make sure you have ``tox`` installed which
can be installed using ``pip``.

.. code:: bash

    pip install tox

Now by simply running ``tox`` from the project root you will have environments
for all the supported Python versions. These will be in the ``.tox`` directory.

To create a specific Python dev environment just make a virtualenv for your Python
version and then install the appropriate ``test-requirements`` file.

For example, setting up Python 3:

.. code:: bash

    pyvenv venv
    source venv/bin/activate
    pip install -r test-requirements.txt


Adding `diff-quality`` Support for a New Quality Checker

Adding support for a new quality checker is simple. diff-quality supports
plugins using the popular Python
pluggy package.

If the quality checker is already implemented as a Python package, great! If not,
create a Python package
to host the plugin implementation.

In the Python package's setup.py file, define an entry point for the plugin,
e.g.

.. code:: python
setup(
...
entry_points={
'diff_cover': [
'sqlfluff = sqlfluff.diff_quality_plugin'
],
},
...
)

Notes:

• The dictionary key for the entry point must be named diff_cover
• The value must be in the format TOOL_NAME = YOUR_PACKAGE.PLUGIN_MODULE

When your package is installed,diff-quality uses this information to
look up the tool package and module based on the tool name provided to the
--violations option of the diff-quality command, e.g.:

.. code:: bash
$ diff-quality --violations sqlfluff

The plugin implementation will look something like the example below. This is
a simplified example based on a working plugin implementation.

.. code:: python
from diff_cover.hook import hookimpl as diff_cover_hookimpl
from diff_cover.violationsreporters.base import BaseViolationReporter, Violation

class SQLFluffViolationReporter(BaseViolationReporter):
    supported_extensions = ['sql']

    def __init__(self):
        super(SQLFluffViolationReporter, self).__init__('sqlfluff')

    def violations(self, src_path):
        return [
            Violation(violation.line_number, violation.description)
            for violation in get_linter().get_violations(src_path)
        ]

    def measured_lines(self, src_path):
        return None

    @staticmethod
    def installed():
        return True


@diff_cover_hookimpl
def diff_cover_report_quality():
    return SQLFluffViolationReporter()

Important notes:

• diff-quality is looking for a plugin function:
  • Located in your package's module that was listed in the setup.py entry point.
  • Marked with the @diff_cover_hookimpl decorator
  • Named diff_cover_report_quality. (This distinguishes it from any other
    plugin types diff_cover may support.)
• The function should return an object with the following properties and methods:
  • supported_extensions property with a list of supported file extensions
  • violations() function that returns a list of Violation objects for
    the specified src_path. For more details on this function and other
    possible reporting-related methods, see the BaseViolationReporter class
    here.

Special Thanks

Shout out to the original author of diff-cover Will Daly <https://github.com/wedaly>_ and the original author of diff-quality Sarina Canelake <https://github.com/sarina>_.

Originally created with the support of edX <https://github.com/edx>_.

.., pypi-version, image:: https://img.shields.io/pypi/v/diff-cover.svg
:target: https://pypi.org/project/diff-cover
:alt: PyPI version
.., conda-version, image:: https://img.shields.io/conda/vn/conda-forge/diff-cover.svg
:target: https://anaconda.org/conda-forge/diff-cover
:alt: Conda version
.., build-status, image:: https://travis-ci.org/Bachmann1234/diff-cover.png
:target: https://travis-ci.org/Bachmann1234/diff-cover
:alt: Build Status
.., coverage-status, image:: https://coveralls.io/repos/github/Bachmann1234/diff-cover/badge.svg?branch=master
:target: https://coveralls.io/github/Bachmann1234/diff-cover?branch=master
:alt: Coverage Status
.., docs-status, image:: https://readthedocs.org/projects/diff-cover/badge/
:alt: Documentation Status
:scale: 100%
:target: http://diff-cover.readthedocs.org/en/latest/