diff --git a/buildspec-unittests.yml b/buildspec-unittests.yml
index 3e7861cbca..8732090421 100644
--- a/buildspec-unittests.yml
+++ b/buildspec-unittests.yml
@@ -7,11 +7,11 @@ phases:
       - TOX_PARALLEL_NO_SPINNER=1
       - PY_COLORS=0
       - start_time=`date +%s`
-      - tox -e flake8,pylint,twine,black-check
+      - tox -e flake8,pylint,twine,black-check --parallel all
       - ./ci-scripts/displaytime.sh 'flake8,pylint,twine,black-check' $start_time
 
       - start_time=`date +%s`
-      - tox -e sphinx,doc8
+      - tox -e sphinx,doc8 --parallel all
       - ./ci-scripts/displaytime.sh 'sphinx,doc8' $start_time
 
       # run unit tests
diff --git a/tox.ini b/tox.ini
index 71762c210b..b26e390822 100644
--- a/tox.ini
+++ b/tox.ini
@@ -67,9 +67,11 @@ passenv =
 # {posargs} can be passed in by additional arguments specified when invoking tox.
 # Can be used to specify which tests to run, e.g.: tox -- -s
 commands =
-    coverage run --source sagemaker -m pytest {posargs}
+    pytest --cov=sagemaker --cov-append {posargs}
     {env:IGNORE_COVERAGE:} coverage report --fail-under=86 --omit */tensorflow/tensorflow_serving/*
 deps = .[test]
+depends =
+    {py27,py36,py37,py38}: clean
 
 [testenv:flake8]
 basepython = python3
@@ -130,3 +132,8 @@ basepython = python3
 deps = black==19.10b0
 commands =
     black -l 100 --check ./
+
+[testenv:clean]
+deps = coverage
+skip_install = true
+commands = coverage erase