How to specify the constraints file for a test?

[brendan-morin]

Let's say I have a package that has install_requires=[pyspark >= 3.0] (among other requirements). I want to run tests on this package, but enforce a constraint on the install of it into the test environment. Let's say I want to constrain to pyspark=3.2.0, but allow the other requirements to resolve as they would naturally.

I tried passing in a constraints file with this constraint to deps and setting constrain_package_deps=true, but I get the error ERROR: Constraints cannot have extras. I checked {env}/constraints.txt, and I see it listed all of my unpinned requirements from install_requires in there (including one with extras, hence the error). That feels like not at all what I am looking for.

Is there a way to specify exactly what ends up in constraints.txt?

[brendan-morin]

Weirdly, it seems like the best way I've found to do this is to actually pre-install my constraints file as part of deps, rather than using it as a constraint:

deps =  -r requirements/test-constraints.txt

If I use it as an actual constraint (-c) in deps, it's overridden by the subsequent package install.

I don't want to use all of the dependencies in deps as my constraints (which seems to be my other option), since those are my test dependencies. If anything, those should be constrained based on my package dependencies. Ideally, the constraint chain should follow:

user defined constraints file -> constrains package deps -> constrains test deps

Am I misunderstanding how this works? It seems like the above workaround is the only way to get what I'm looking for.

[brendan-morin]

Yes, I read this, and from what I can tell, the described use case is not addressed. The problem is that not every install command tox does seems to allow passing flags to pip. If I were to replicate what I would intend to be done, in pure pip commands:

# install the library and all requirements, as a user might + constraints
pip install . -c my_constraint.txt

# freeze the venv to use this as a constraint for test requirements
# we want to do this because the test requirements should not be able to
# modify or override the install requirements
pip freeze > test_constraints.txt

# we now have a constraint file that represents a real world constrained 
# install - now we install the test requirements around that (pytest, linters, etc)
pip install -r test_requirements.txt -c test_constraints.txt

[brendan-morin]

I don't expect to pip freeze in the middle of tox's workflow, but I've added that in to demonstrate the intent is to constrain the library install (as a user might) and then test that state, while avoiding test requirements from mutating this state.

[brendan-morin]

I'm currently exploring if the install_command is appropriate... some more documentation on this might be helpful. Currently trying:

install_command = python -I -m pip install <opts> <packages> -c my_constraints.txt

But that doesn't seem to substitute the packages into <packages>, but rather insert it after. I've also tried {packages}, both fail like:

'python -I -m pip install {opts} {packages} -c my_constraints.txt' coverage pytest ... (etc)

[brendan-morin]

install_command is the answer. Using constrain_package_deps or use_frozen_constraints was barking up the wrong tree. It wasn't explicit in the documentation, but this is applied to both dep and package installs. If using this in tox.ini, this will work:

install_command =
    python -I -m pip install {opts} {packages} -c my_constraints.txt

The only thing that would be one better would be being able to have separate install commands for deps and package installs (so they can get their own constraints). Perhaps a feature request.

[gaborbernat]

install_command is deprecated, you should use setting environment variables instead to control pip via PIP_ 😊 one of the reasons we removed https://tox.wiki/en/4.6.4/upgrading.html#cli-arguments-changed the --index-url flag.

[brendan-morin]

I read through the docs there, but I'm not sure I understand what actionable next steps are. Any chance you could help me understand how I could use PIP_ for the above use case instead of install_command? Also maybe I'm just bad at searching, but I don't see where theres mention in the docs about install_command being deprecated.

[gaborbernat]

This should be equivalent:

set_env = 
	PIP_CONSTRAINT=my_constraints.txt

Also maybe I'm just bad at searching, but I don't see where theres mention in the docs about install_command being deprecated.

Yeah, TBD, but I do plan to drop it.

[brendan-morin]

Great! That does appear to work, thank you. One (minor) downside I'm noting vs install_command is that this constraints file is no longer mentioned in the logs. Perhaps an extra log setting to output PIP_ vars used could be a helpful (though there may be some security concerns, e.g. username/passwords in index URLs), or something similar just to confirm that what we think is happening is actually happening.