Pytest added new dependencies that were not specified in the requirements.txt. Somehow I got into situation that new pytest was installed without installing its dependency atomicwrites and tests failed.
Add new pytest dependecies to the pinned
requirements files.
Add linting dev-dependencies so linting can be used in IDEs.
Add also the package itself to the dev-requirements so it is findable
when running pytests.
Specify requirements.txt as constraints for dev-requirements.
Pytest added new dependencies that were not specified in the requirements.txt. Somehow I got into situation that new pytest was installed without installing its dependency atomicwrites and tests failed.