Tox

When using tox you can have ultra-compact configuration - you can have all of it in tox.ini:

[tox]
envlist = ...

[tool:pytest]
...

[coverage:paths]
...

[coverage:run]
...

[coverage:report]
..

[testenv]
commands = ...

An usual problem users have is that pytest-cov will erase the previous coverage data by default, thus if you run tox with multiple environments you’ll get incomplete coverage at the end.

To prevent this problem you need to use --cov-append. It’s still recommended to clean the previous coverage data to have consistent output. A tox.ini like this should be enough for sequential runs:

[tox]
envlist = clean,py27,py36,...

[testenv]
commands = pytest --cov --cov-append --cov-report=term-missing ...
deps =
    pytest
    pytest-cov

[testenv:clean]
deps = coverage
skip_install = true
commands = coverage erase

For parallel runs we need to set some dependencies and have an extra report env like so:

[tox]
envlist = clean,py27,py36,report

[testenv]
commands = pytest --cov --cov-append --cov-report=term-missing
deps =
    pytest
    pytest-cov
depends =
    {py27,py36}: clean
    report: py27,py36

[testenv:report]
deps = coverage
skip_install = true
commands =
    coverage report
    coverage html

[testenv:clean]
deps = coverage
skip_install = true
commands = coverage erase

Depending on your project layout you might need extra configuration, see the working examples at https://github.com/pytest-dev/pytest-cov/tree/master/examples for two common layouts.