diff --git a/swh/objstorage/tests/test_server.py b/swh/objstorage/tests/test_server.py
index 77f2ccf..165b658 100644
--- a/swh/objstorage/tests/test_server.py
+++ b/swh/objstorage/tests/test_server.py
@@ -1,126 +1,116 @@
 # Copyright (C) 2019  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import copy
 
 import pytest
 import yaml
 
 from swh.objstorage.api.server import load_and_check_config
 
 
 def prepare_config_file(tmpdir, content, name="config.yml"):
     """Prepare configuration file in `$tmpdir/name` with content `content`.
 
     Args:
         tmpdir (LocalPath): root directory
         content (str/dict): Content of the file either as string or as a dict.
                             If a dict, converts the dict into a yaml string.
         name (str): configuration filename
 
     Returns
         path (str) of the configuration file prepared.
 
     """
     config_path = tmpdir / name
     if isinstance(content, dict):  # convert if needed
         content = yaml.dump(content)
     config_path.write_text(content, encoding="utf-8")
     # pytest on python3.5 does not support LocalPath manipulation, so
     # convert path to string
     return str(config_path)
 
 
 def test_load_and_check_config_no_configuration():
     """Inexistent configuration files raises"""
-    with pytest.raises(EnvironmentError) as e:
+    with pytest.raises(EnvironmentError, match="Configuration file must be defined"):
         load_and_check_config(None)
 
-    assert e.value.args[0] == "Configuration file must be defined"
-
     config_path = "/indexer/inexistent/config.yml"
-    with pytest.raises(FileNotFoundError) as e:
+    with pytest.raises(FileNotFoundError, match=f"{config_path} does not exist"):
         load_and_check_config(config_path)
 
-    assert e.value.args[0] == "Configuration file %s does not exist" % (config_path,)
-
 
 def test_load_and_check_config_invalid_configuration_toplevel(tmpdir):
     """Invalid configuration raises"""
     config = {"something": "useless"}
     config_path = prepare_config_file(tmpdir, content=config)
-    with pytest.raises(KeyError) as e:
+    with pytest.raises(KeyError, match="missing objstorage config entry"):
         load_and_check_config(config_path)
 
-    assert e.value.args[0] == "Invalid configuration; missing objstorage config entry"
-
 
 def test_load_and_check_config_invalid_configuration(tmpdir):
     """Invalid configuration raises"""
     config_path = prepare_config_file(
         tmpdir, content={"objstorage": {"something": "useless"}}
     )
-    with pytest.raises(KeyError) as e:
+    with pytest.raises(KeyError, match="missing cls config entry"):
         load_and_check_config(config_path)
 
-    assert "missing cls config entry" in e.value.args[0]
-
 
 def test_load_and_check_config_invalid_configuration_level2(tmpdir):
     """Invalid configuration at 2nd level raises"""
     config = {
         "objstorage": {
             "cls": "pathslicing",
             "args": {"root": "root", "slicing": "slicing",},
             "client_max_size": "10",
         }
     }
     for key in ("root", "slicing"):
         c = copy.deepcopy(config)
         c["objstorage"]["args"].pop(key)
         config_path = prepare_config_file(tmpdir, c)
-        with pytest.raises(KeyError) as e:
+        with pytest.raises(KeyError, match=f"missing {key} config entry"):
             load_and_check_config(config_path)
 
-        assert "missing %s config entry" % key in e.value.args[0]
-
 
 def test_load_and_check_config_fine(tmpdir):
     """pathslicing configuration fine loads ok"""
     config = {
         "objstorage": {
             "cls": "pathslicing",
             "args": {"root": "root", "slicing": "slicing",},
         }
     }
 
     config_path = prepare_config_file(tmpdir, config)
     cfg = load_and_check_config(config_path)
     assert cfg == config
 
 
 def test_load_and_check_config_no_args(tmpdir):
     """pathslicing configuration with no args key loads ok"""
     config = {
         "objstorage": {"cls": "pathslicing", "root": "root", "slicing": "slicing"}
     }
 
     config_path = prepare_config_file(tmpdir, config)
     cfg = load_and_check_config(config_path)
     assert cfg == config
 
 
 def test_load_and_check_config_fine2(tmpdir):
     config = {"client_max_size": "10", "objstorage": {"cls": "memory", "args": {}}}
     config_path = prepare_config_file(tmpdir, config)
     cfg = load_and_check_config(config_path)
     assert cfg == config
 
 
 def test_load_and_check_config_only_cls(tmpdir):
     config = {"client_max_size": "10", "objstorage": {"cls": "memory"}}
     config_path = prepare_config_file(tmpdir, config)
     cfg = load_and_check_config(config_path)
     assert cfg == config