Let's try this way

tox.ini

@@ -16,7 +16,7 @@ commands =
     {toxinidir}/src/memopol/bin/install_client_deps.sh
     cp {toxinidir}/src/memopol/tests/local_settings.py {toxinidir}/src/memopol/local_settings.py
     py.test src/
-    createdb -U memopol_test -p 5433 $CI_BUILD_REF_NAME
+    bash -c 'createdb -U memopol_test -p 5433 $CI_BUILD_REF_NAME'
     memopol migrate
     bash -c 'cat src/representatives/contrib/francedata/tests/representatives_input.json | francedata_import_representatives'
     bash -c 'cat src/representatives/contrib/parltrack/tests/representatives_fixture.json | parltrack_import_representatives'
@@ -25,7 +25,7 @@ commands =
     bash -c 'cat src/representatives_votes/contrib/francedata/tests/votes_input.json | francedata_import_votes'
     bash -c 'cat src/representatives_votes/contrib/parltrack/tests/dossiers_fixture.json | parltrack_import_dossiers'
     bash -c 'cat src/representatives_votes/contrib/parltrack/tests/votes_fixture.json | parltrack_import_votes'
-    dropdb -U memopol_test -p 5433 $CI_BUILD_REF_NAME
+    bash -c 'dropdb -U memopol_test -p 5433 $CI_BUILD_REF_NAME'
 
 whitelist_externals =
     psql