WIP: Test impact of plugin installation

This aims to create a tox environment that tests that installation of
popular plugins does not break pytest.

Author: ssbarnea

.github/workflows/main.yml

@@ -111,6 +111,12 @@ jobs:
             tox_env: "py38-xdist"
             use_coverage: true
 
+          - name: "py37-plugins"
+            python: "3.7"
+            os: ubuntu-latest
+            tox_env: "py37-plugins"
+            use_coverage: true
+
           - name: "docs"
             python: "3.7"
             os: ubuntu-latest

tox.ini

@@ -11,7 +11,7 @@ envlist =
     py38
     py39
     pypy3
-    py37-{pexpect,xdist,unittestextras,numpy,pluggymaster}
+    py37-{pexpect,xdist,unittestextras,numpy,pluggymaster,plugins}
     doctesting
     py37-freeze
     docs
@@ -53,6 +53,8 @@ deps =
     unittestextras: twisted
     unittestextras: asynctest
     xdist: pytest-xdist>=1.13
+    plugins: pytest-cov
+    plugins: pytest-xdist
     {env:_PYTEST_TOX_EXTRA_DEP:}
 
 [testenv:linting]