Switch to stestr.

CI is broken due to a bug [0] reported
in testr.

Following approach used in keystone and switching
to stestr instead of testr.

[0] https://review.opendev.org/#/c/662582/
[1] d1e3a7845d

Change-Id: I108b4d7b4c4f20f4b077077528f07f9447747a48
Signed-off-by: Jorge Niedbalski <jorge.niedbalski@canonical.com>

.stestr.conf

@@ -0,0 +1,3 @@
+[DEFAULT]
+test_path=./unit_tests
+top_dir=./

.testr.conf

@@ -1,8 +0,0 @@
-[DEFAULT]
-test_command=OS_STDOUT_CAPTURE=${OS_STDOUT_CAPTURE:-1} \
-             OS_STDERR_CAPTURE=${OS_STDERR_CAPTURE:-1} \
-             OS_TEST_TIMEOUT=${OS_TEST_TIMEOUT:-60} \
-             ${PYTHON:-python} -m subunit.run discover -t ./ ./unit_tests $LISTOPT $IDOPTION
-
-test_id_option=--load-list $IDFILE
-test_list_option=--list

test-requirements.txt

@@ -1,6 +1,6 @@
 # Lint and unit test requirements
 flake8
-os-testr>=0.4.1
+stestr>=2.2.0
 charms.reactive
 mock>=1.2
 coverage>=3.6

tox.ini

@@ -13,12 +13,12 @@ install_command =
 [testenv:py35]
 basepython = python3
 deps = -r{toxinidir}/test-requirements.txt
-commands = ostestr {posargs}
+commands = stestr run {posargs}
 
 [testenv:py36]
 basepython = python3.6
 deps = -r{toxinidir}/test-requirements.txt
-commands = ostestr {posargs}
+commands = stestr run {posargs}
 
 [testenv:pep8]
 basepython = python3
@@ -35,7 +35,7 @@ setenv =
     PYTHON=coverage run
 commands =
     coverage erase
-    ostestr {posargs}
+    stestr run {posargs}
     coverage combine
     coverage html -d cover
     coverage xml -o cover/coverage.xml