tests,tox: do test each 'extra' environment in a dedicated venv

to make sure each extra setup dependencies are ok.
This requires to move test files in its related subpackage.

swh/core/tests/test_db.py → swh/core/db/tests/test_db.py

@@ -11,7 +11,7 @@ from hypothesis import strategies, given
 import pytest
 
 from swh.core.db import BaseDb
-from swh.core.tests.db_testing import (
+from .db_testing import (
     SingleDbTestFixture, db_create, db_destroy, db_close,
 )
 

tox.ini

 [tox]
-envlist=flake8,py3
+envlist=flake8,py3-{core,db,server}
 
-[testenv:py3]
+[testenv:py3-core]
 deps =
-  .[testing]
-  pytest-cov
+  -rrequirements-test.txt
+  .
+commands =
+  pytest --doctest-modules swh/core/tests {posargs}
+
+[testenv:py3-db]
+deps =
+  -rrequirements-test.txt
+  .[db]
   pifpaf
 commands =
-  pifpaf run postgresql -- pytest --doctest-modules --hypothesis-profile=fast --cov=swh --cov-branch {posargs}
+  pifpaf run postgresql -- \
+    pytest swh/core/db/tests {posargs}
 
-[testenv:py3-slow]
+[testenv:py3-server]
+deps =
+  -rrequirements-test.txt
+  .[http]
+commands =
+  pytest swh/core/api/tests {posargs}
+
+[testenv:py3]
 deps =
   .[testing]
   pytest-cov
   pifpaf
 commands =
-  pifpaf run postgresql -- pytest --doctest-modules --hypothesis-profile=slow --cov=swh --cov-branch {posargs}
-
+  pifpaf run postgresql -- \
+    pytest --doctest-modules \
+	       --hypothesis-profile=slow \
+	       --cov=swh --cov-branch \
+		   {posargs}
 
 [testenv:flake8]
 skip_install = true