Add tox configurations

Fixes: #295

tox.ini

@@ -0,0 +1,45 @@
+[tox]
+minversion = 3.9.0
+envlist =
+    lint
+    docs
+    py{36,37,38,39}
+isolated_build = True
+
+[testenv]
+description = Run unit-testing
+# develop temporary disabled as project packaging does not work with it yet:
+# https://github.com/willmcgugan/rich/issues/345
+usedevelop = False
+deps =
+    -r requirements-dev.txt
+# do not put * in passenv as it may break builds due to reduced isolation
+passenv =
+    CI
+    GITHUB_*
+    HOME
+    PYTEST_*
+    SSH_AUTH_SOCK
+    TERM
+setenv =
+    PYTHONDONTWRITEBYTECODE=1
+    PYTHONUNBUFFERED=1
+commands =
+    # failsafe as older pip may install incompatible dependencies
+    pip check
+    pytest --cov-report term-missing --cov=rich tests/ {posargs}
+
+[testenv:lint]
+description = Runs all linting tasks
+commands =
+    black .
+    mypy -p rich --ignore-missing-imports --warn-unreachable
+skip_install = true
+
+[testenv:docs]
+description = Builds documentation
+changedir = docs
+deps =
+    -r docs/requirements.txt
+commands =
+    sphinx-build -M html source build