Add black to lint job

And rename tox' "mypy" env to "lint".

.github/workflows/test.yml

@@ -27,7 +27,7 @@ jobs:
     - name: Install packages
       run: pip install tox
     - name: Run Tox
-      run: tox -e mypy,package_readme
+      run: tox -e lint,package_readme
 
   test:
     runs-on: ${{ matrix.platform }}

dev-requirements.txt

@@ -3,3 +3,6 @@ tox>=2.5
 bump2version>=0.5.6
 sphinx>=1.5.5
 mypy>=0.782
+
+# Pin black as each version could change formatting, breaking CI randomly.
+black==22.12.0

pyproject.toml

@@ -0,0 +1,2 @@
+[tool.black]
+target-version = ["py37"]

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 minversion = 3.0
-envlist = mypy, py3{7,8,9,10,11}-cov, htmlcov
+envlist = lint, py3{7,8,9,10,11}-cov, htmlcov
 skip_missing_interpreters=true
 
 [testenv]
@@ -41,11 +41,12 @@ commands =
     coverage combine
     coverage html
 
-[testenv:mypy]
+[testenv:lint]
 deps =
     -r dev-requirements.txt
 skip_install = true
 commands =
+    black --check --diff .
     mypy
 
 [testenv:codecov]