tox: testenv: use single command, settings via env

Author: blueyed

tox.ini

@@ -35,16 +35,18 @@ setenv =
     COV_CORE_CONFIG={toxinidir}/.coveragerc
     COV_CORE_DATAFILE={toxinidir}/.coverage.eager
 
+    mysql_innodb: DJANGO_SETTINGS_MODULE=pytest_django_test.settings_mysql_innodb
+    mysql_myisam: DJANGO_SETTINGS_MODULE=pytest_django_test.settings_mysql_myisam
+    postgres:     DJANGO_SETTINGS_MODULE=pytest_django_test.settings_postgres
+    sqlite:       DJANGO_SETTINGS_MODULE=pytest_django_test.settings_sqlite
+    sqlite_file:  DJANGO_SETTINGS_MODULE=pytest_django_test.settings_sqlite_file
+
 passenv = PYTEST_ADDOPTS
 usedevelop = True
 commands =
     checkqa: flake8 --version
     checkqa: flake8 --show-source --statistics {posargs:pytest_django pytest_django_test}
-    mysql_innodb: pytest --ds=pytest_django_test.settings_mysql_innodb --strict {posargs:tests}
-    mysql_myisam: pytest --ds=pytest_django_test.settings_mysql_myisam --strict {posargs:tests}
-    postgres: pytest --ds=pytest_django_test.settings_postgres --strict {posargs:tests}
-    sqlite: pytest --ds=pytest_django_test.settings_sqlite --strict {posargs:tests}
-    sqlite_file: pytest --ds=pytest_django_test.settings_sqlite_file --strict {posargs:tests}
+    pytest --strict {posargs:tests}
 
 [testenv:doc8]
 basepython = python3.6