Add build+twine test to tox

Allows local twine validation of build
before sending it to GitHub CI

setup.cfg

@@ -60,7 +60,7 @@ test =
 universal = 1
 
 [tox:tox]
-envlist = linters, py36, py37, py38, py39, coverage-report
+envlist = linters, twine, py36, py37, py38, py39, coverage-report
 isolated_build = True
 requires = tox-conda; platform_system=="Darwin"
 
@@ -90,6 +90,15 @@ commands =
     black --check --diff .
     flake8 --count src tests
 
+[testenv:twine]
+deps =
+    build>=0.4.0
+    twine>=3.4.1
+skip_install = true
+commands =
+    python -m build --sdist --wheel .
+    python -m twine check dist/*
+
 [testenv:coverage-report]
 deps = coverage[toml]
 skip_install = true