diff --git a/tox.ini b/tox.ini
index 40517637..8b4db3f0 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,6 +1,6 @@
 [tox]
 envlist =
-    py{27,34,35,36}-{local,integ}-fast,
+    py{27,34,35,36}-{local,integ}-fast, nocmk,
     bandit, doc8, readme,
     flake8, pylint,
     flake8-tests, pylint-tests,
@@ -25,18 +25,31 @@ passenv =
 sitepackages = False
 deps = -rtest/requirements.txt
 commands =
+    # Only run small test scenario sets
     local-fast: {[testenv:base-command]commands} -m "local and not slow and not veryslow and not nope"
     integ-fast: {[testenv:base-command]commands} -m "integ and not slow and not veryslow and not nope"
     all-fast: {[testenv:base-command]commands} -m "not slow and not veryslow and not nope"
+    # Also run moderately large test scenario sets
     local-slow: {[testenv:base-command]commands} -m "local and not veryslow and not nope"
     integ-slow: {[testenv:base-command]commands} -m "integ and not veryslow and not nope"
     all-slow: {[testenv:base-command]commands} -m "not veryslow and not nope"
+    # Also run very large test scenario sets
     local-full: {[testenv:base-command]commands} -m "local and not nope"
     integ-full: {[testenv:base-command]commands} -m "integ and not nope"
     all-full: {[testenv:base-command]commands} -m "not nope"
+    # Only run extremely large test scenario sets
     local-nope: {[testenv:base-command]commands} -m "local and nope"
     integ-nope: {[testenv:base-command]commands} -m "integ and nope"
     all-nope: {[testenv:base-command]commands} -m "nope"
+    # Do not select any specific markers
+    manual: {[testenv:base-command]commands}
+
+# Verify that local tests work without environment variables present
+[testenv:nocmk]
+basepython = python3
+sitepackages = False
+deps = -rtest/requirements.txt
+commands = {[testenv:base-command]commands} -m "local and not slow and not veryslow and not nope"
 
 # mypy
 [testenv:mypy-coverage]