The previous test configuration made it difficult to run a single test
with the pytest CLI. There were two major issues:
- The Tests directory was not a package. It now includes a __init__.py
file and imports from other tests modules are done with relative
imports.
- setup.cfg always specified the Tests directory. So even if a specific
test were specified as a CLI arg, this configuration would also always
include all tests. This configuration has been removed to allow
specifying a single test on the command line.
Contributors can now run specific tests with a single command such as:
$ tox -e py37 -- Tests/test_file_pdf.py::TestFilePdf.test_rgb
This makes it easy and faster to iterate on a single test failure and is
very familiar to those that have previously used tox and pytest.
When running tox or pytest with no arguments, they still discover and
runs all tests in the Tests directory.
Allows contributors to easily run the lint stage with a single command:
`tox -e lint`. This creates shorter round trips with CI in case of an
error.
Update the Travis configuration to use the new environment to run lint.
This allows using a single/common source of truth to reduce differences
between Travis and local testing.
The tox environment uses the skip_install feature as static analysis
doesn't requiring install the Pillow package itself to run. This feature
requires tox 1.9 (2015-02-24), so a minimum tox version was added to the
configuration.
https://tox.readthedocs.io/en/latest/config.html#conf-skip_install
