benchmark| Add benchmarking option to tox

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py35, py36, py37, py38, pypy, pylint
+envlist = py35, py36, py37, py38, pypy, pylint, benchmark
 skip_missing_interpreters = true
 
 [testenv:pylint]
@@ -53,12 +53,14 @@ deps =
    mccabe
    pytest
    pytest-xdist
+   pytest-benchmark
 
 setenv =
     COVERAGE_FILE = {toxinidir}/.coverage.{envname}
 
 commands =
-    python -Wignore -m coverage run -m pytest {toxinidir}/tests/ {posargs:}
+    ; Run tests, ensuring all benchmark tests do not run
+    python -Wignore -m coverage run -m pytest --benchmark-disable {toxinidir}/tests/ {posargs:}
 
     ; Transform absolute path to relative path
     ; for compatibility with coveralls.io and fix 'source not available' error.
@@ -131,3 +133,29 @@ commands =
   rm -f extensions.rst
   python ./exts/pylint_extensions.py
   sphinx-build -W -b html -d _build/doctrees . _build/html
+
+[testenv:benchmark]
+deps =
+   https://github.com/PyCQA/astroid/tarball/master#egg=astroid-master-2.0
+   coverage<5.0
+   isort
+   mccabe
+   pytest
+   pytest-xdist
+   pygal
+   pytest-benchmark
+
+commands =
+    ; Run the only the benchmark tests, grouping output and forcing .json output so we
+    ; can compare benchmark runs
+    python -Wi -m pytest --exitfirst \
+                         --failed-first \
+                         --benchmark-only \
+                         --benchmark-save=batch_files \
+                         --benchmark-save-data \
+                         --benchmark-autosave \
+                         {toxinidir}/tests \
+                         --benchmark-group-by="group" \
+                         {posargs:}
+
+changedir = {toxworkdir}