ci: add a tox environment to run the test

Author: james-garner-canonical

tox.ini

@@ -103,6 +103,10 @@ commands =
     pip install pylxd
     python -m pytest --tb native -ra -v -s {posargs:-m 'serial'}
 
+[testenv:validate]
+envdir = {toxworkdir}/validate
+commands = python -m pytest --tb native -ra -v tests/validate
+
 [testenv:example]
 envdir = {toxworkdir}/py3
 commands = python {posargs}