Improve tox config and add isort formatter

tox.ini

@@ -1,27 +1,37 @@
 [tox]
 envlist=
     black,
+    sort,
     lint,
     py36,
     py37,
     py38,
     py39,
 
 [testenv]
+; SQL Alchemy 2.0 migration
+setenv = SQLALCHEMY_WARN_20=1
 deps = -rrequirements-dev.txt
 commands =
     coverage erase
-    pytest --junitxml=test-reports/junit.xml --cov={toxinidir}/comet --cov={toxinidir}/comet_core/ --cov-report=term --cov-report=xml:test-reports/cobertura.xml {toxinidir}/tests/
+    pytest --junitxml=test-reports/junit.xml --cov={toxinidir}/comet_core/ --cov-report=term --cov-report=xml:test-reports/cobertura.xml {toxinidir}/tests/
 
-[testenv:black]
+[testenv:format]
 basepython = python3.6
 deps = -rrequirements-dev.txt
 skip_install = true
 commands =
-    black . --diff --check
+    python3 -m black --diff --check {toxinidir}/comet_core/ {toxinidir}/tests
+
+[testenv:isort]
+basepython = python3.6
+deps = -rrequirements-dev.txt
+skip_install = true
+commands =
+    python3 -m isort --diff --check-only  {toxinidir}/comet_core/ {toxinidir}/tests
 
 [testenv:lint]
 basepython = python3.6
 deps = -rrequirements-dev.txt
 commands =
-    pylint --rcfile={toxinidir}/.pylintrc comet_core
+    python3 -m pylint --rcfile={toxinidir}/.pylintrc {toxinidir}/comet_core {toxinidir}/tests