Update tox.ini

Signed-off-by: Hiroshi Miura <miurahr@linux.com>

tox.ini

@@ -1,14 +1,14 @@
 [tox]
-envlist = clean, mypy, check, pypy3, py{35,36,37}, bench, report, docs
+envlist = clean, mypy, check, pypy3, py{35,36,37,38}, bench, report, docs
 
 [testenv]
 passenv = TRAVIS TRAVIS_* APPVEYOR APPVEYOR_*
 deps = -rrequirements.txt
 commands =
     python -m pytest -vv
 depends =
-    py{35,36,37}: clean, check
-    bench: py{35,36,37}
+    pypy3,py{35,36,37,38}: clean, check
+    bench: py{35,36,37,38}
 
 [flake8]
 ignore = F841
@@ -18,6 +18,7 @@ basepython =
     py35: python3.5
     py36: python3.6
     py37: python3.7
+    py38: python3.8
     pypy3: pypy3
 python_files = test*.py
 addopts = --benchmark-autosave --cov-report=term-missing:skip-covered --cov-append --cov=py7zr
@@ -45,6 +46,7 @@ strict_optional = True
 show_column_numbers = True
 
 [testenv:check]
+basepython = python3.7
 deps =
     docutils
     check-manifest
@@ -64,6 +66,7 @@ skip_install = true
 commands = coverage erase
 
 [testenv:bench]
+basepython = python3.7
 deps = pytest-benchmark
 commands = pytest-benchmark compare
 
@@ -82,6 +85,7 @@ commands =
     sphinx-build -b linkcheck docs dist/docs
 
 [testenv:report]
+basepython = python3.7
 deps = coverage
 skip_install = true
 commands =