pythonPackages.cheroot is broken due to missing dependencies in unstable

[xvapx]

Issue description

cheroot 6.3.2 depends on backports_functools_lru_cache and pytest-testmon to run its tests.

Steps to reproduce

Try to build cheroot 6.3.2 from nixpkgs-unstable (updated in 095a58c)

Technical details

Please run nix-shell -p nix-info --run "nix-info -m" and paste the
results.

• system: "x86_64-linux"
• host os: Linux 4.14.51, NixOS, 18.03.132768.94d80eb7247 (Impala)
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.0.4
• channels(root): ""
• nixpkgs: /nix/store/gsqxmqmpbq40d62z0fnbyih00lgzx0ac-nixexprs.tar.xz

[xvapx]

cc @FRidh
Adding backports_functools_lru_cache to checkInputs works, but testmon is not packaged.
I would disable it, to do it we need to remove the --testmon flag from pytest.ini.
I can remove the flag with substituteInPlace at the start of the checkPhase, can't do in preCheck.
Is there a better way to do it?

[FRidh]

Do it in the postPatch, that is the preferred place for file changes.

[xvapx]

Thanks, done.