diff --git a/MANIFEST.in b/MANIFEST.in
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -6,3 +6,5 @@
 include version.txt
 recursive-include swh/core/sql *.sql
 recursive-include swh py.typed
+recursive-include swh/core/tests/data/ *
+recursive-include swh/core/tests/fixture/data/ *
diff --git a/pytest_swh_core.py b/pytest_swh_core.py
new file mode 100644
--- /dev/null
+++ b/pytest_swh_core.py
@@ -0,0 +1,180 @@
+# 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 logging
+import re
+import pytest
+
+from functools import partial
+from os import path
+from typing import Dict, List, Optional
+from urllib.parse import urlparse
+
+
+logger = logging.getLogger(__name__)
+
+
+# Check get_local_factory function
+# Maximum number of iteration checks to generate requests responses
+MAX_VISIT_FILES = 10
+
+
+def get_response_cb(request, context, datadir,
+                    ignore_urls: List[str] = [],
+                    visits: Optional[Dict] = None):
+    """Mount point callback to fetch on disk the request's content.
+
+    This is meant to be used as 'body' argument of the requests_mock.get()
+    method.
+
+    It will look for files on the local filesystem based on the requested URL,
+    using the following rules:
+
+    - files are searched in the datadir/<hostname> directory
+
+    - the local file name is the path part of the URL with path hierarchy
+      markers (aka '/') replaced by '_'
+
+    Eg. if you use the requests_mock fixture in your test file as:
+
+        requests_mock.get('https://nowhere.com', body=get_response_cb)
+        # or even
+        requests_mock.get(re.compile('https://'), body=get_response_cb)
+
+    then a call requests.get like:
+
+        requests.get('https://nowhere.com/path/to/resource')
+
+    will look the content of the response in:
+
+        datadir/nowhere.com/path_to_resource
+
+    Args:
+        request (requests.Request): Object requests
+        context (requests.Context): Object holding response metadata
+            information (status_code, headers, etc...)
+        ignore_urls: urls whose status response should be 404 even if the local
+            file exists
+        visits: Dict of url, number of visits. If None, disable multi visit
+            support (default)
+
+    Returns:
+        Optional[FileDescriptor] on disk file to read from the test context
+
+    """
+    logger.debug('get_response_cb(%s, %s)', request, context)
+    logger.debug('url: %s', request.url)
+    logger.debug('ignore_urls: %s', ignore_urls)
+    if request.url in ignore_urls:
+        context.status_code = 404
+        return None
+    url = urlparse(request.url)
+    dirname = url.hostname  # pypi.org | files.pythonhosted.org
+    # url.path: pypi/<project>/json -> local file: pypi_<project>_json
+    filename = url.path[1:]
+    if filename.endswith('/'):
+        filename = filename[:-1]
+    filename = filename.replace('/', '_')
+    filepath = path.join(datadir, dirname, filename)
+    if visits is not None:
+        visit = visits.get(url, 0)
+        visits[url] = visit + 1
+        if visit:
+            filepath = filepath + '_visit%s' % visit
+
+    if not path.isfile(filepath):
+        logger.debug('not found filepath: %s', filepath)
+        context.status_code = 404
+        return None
+    fd = open(filepath, 'rb')
+    context.headers['content-length'] = str(path.getsize(filepath))
+    return fd
+
+
+@pytest.fixture
+def datadir(request):
+    """By default, returns the test directory's data directory.
+
+    This can be overriden on a per arborescence basis. Add an override
+    definition in the local conftest, for example:
+
+        import pytest
+
+        from os import path
+
+        @pytest.fixture
+        def datadir():
+            return path.join(path.abspath(path.dirname(__file__)), 'resources')
+
+
+    """
+    return path.join(path.dirname(str(request.fspath)), 'data')
+
+
+def requests_mock_datadir_factory(ignore_urls: List[str] = [],
+                                  has_multi_visit: bool = False):
+    """Fixture factory to allow creation of multiple fixtures implementation.
+
+    The main usage is to look for files on the local filesystem based on the
+    requested URL, using the following rules:
+
+    - files are searched in the datadir/<hostname> directory
+
+    - the local file name is the path part of the URL with path hierarchy
+      markers (aka '/') replaced by '_'
+
+    Multiple implementations possible, for example:
+
+    - requests_mock_datadir_factory([]):
+        This computes the file name from the query and always returns the same
+        result
+
+    - requests_mock_datadir_factory(has_multi_visit=True):
+
+        This computes the file name from the query and returns the content of
+        the filename the first time, the next call returning the content of
+        files suffixed with _visit1 and so on and so forth. If the file is not
+        found, returns a 404.
+
+    - requests_mock_datadir_factory(
+        ignore_urls=['url1', 'url2']):
+
+        This will ignore any files corresponding to url1 and url2, always
+        returning 404.
+
+    Args:
+        ignore_urls: List of urls to always returns 404 (whether file exists or
+            not)
+        has_multi_visit: Activate or not the multiple visits behavior
+
+    """
+    @pytest.fixture
+    def requests_mock_datadir(requests_mock, datadir):
+        if not has_multi_visit:
+            cb = partial(get_response_cb,
+                         ignore_urls=ignore_urls,
+                         datadir=datadir)
+            requests_mock.get(re.compile('https://'), body=cb)
+        else:
+            visits = {}
+            requests_mock.get(re.compile('https://'), body=partial(
+                get_response_cb, ignore_urls=ignore_urls, visits=visits,
+                datadir=datadir)
+            )
+
+        return requests_mock
+
+    return requests_mock_datadir
+
+
+# Default `requests_mock_datadir` implementation
+requests_mock_datadir = requests_mock_datadir_factory([])
+
+# Implementation for multiple visits behavior:
+# - first time, it checks for a file named `filename`
+# - second time, it checks for a file named `filename`_visit1
+# etc...
+requests_mock_datadir_visits = requests_mock_datadir_factory(
+    has_multi_visit=True)
diff --git a/setup.py b/setup.py
old mode 100644
new mode 100755
--- a/setup.py
+++ b/setup.py
@@ -46,6 +46,7 @@
     author_email='swh-devel@inria.fr',
     url='https://forge.softwareheritage.org/diffusion/DCORE/',
     packages=find_packages(),
+    py_modules=['pytest_swh_core'],
     scripts=[],
     install_requires=parse_requirements(None, 'swh'),
     setup_requires=['vcversioner'],
@@ -63,6 +64,8 @@
         [swh.cli.subcommands]
         db=swh.core.cli.db:db
         db-init=swh.core.cli.db:db_init
+        [pytest11]
+        pytest_swh_core = pytest_swh_core
     ''',
     classifiers=[
         "Programming Language :: Python :: 3",
diff --git a/swh/core/tests/data/example.com/file.json b/swh/core/tests/data/example.com/file.json
new file mode 100644
--- /dev/null
+++ b/swh/core/tests/data/example.com/file.json
@@ -0,0 +1,3 @@
+{
+    "hello": "you"
+}
diff --git a/swh/core/tests/data/example.com/file.json_visit1 b/swh/core/tests/data/example.com/file.json_visit1
new file mode 100644
--- /dev/null
+++ b/swh/core/tests/data/example.com/file.json_visit1
@@ -0,0 +1,3 @@
+{
+    "hello": "world"
+}
diff --git a/swh/core/tests/data/example.com/other.json b/swh/core/tests/data/example.com/other.json
new file mode 100644
--- /dev/null
+++ b/swh/core/tests/data/example.com/other.json
@@ -0,0 +1 @@
+"foobar"
diff --git a/swh/core/tests/fixture/__init__.py b/swh/core/tests/fixture/__init__.py
new file mode 100644
diff --git a/swh/core/tests/fixture/conftest.py b/swh/core/tests/fixture/conftest.py
new file mode 100644
--- /dev/null
+++ b/swh/core/tests/fixture/conftest.py
@@ -0,0 +1,16 @@
+# 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 pytest
+
+from os import path
+
+
+DATADIR = path.join(path.abspath(path.dirname(__file__)), 'data')
+
+
+@pytest.fixture
+def datadir():
+    return DATADIR
diff --git a/swh/core/tests/fixture/data/example.com/file.json b/swh/core/tests/fixture/data/example.com/file.json
new file mode 100644
--- /dev/null
+++ b/swh/core/tests/fixture/data/example.com/file.json
@@ -0,0 +1,3 @@
+{
+    "welcome": "you"
+}
diff --git a/swh/core/tests/fixture/test_pytest_plugin.py b/swh/core/tests/fixture/test_pytest_plugin.py
new file mode 100644
--- /dev/null
+++ b/swh/core/tests/fixture/test_pytest_plugin.py
@@ -0,0 +1,25 @@
+# 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 requests
+
+from .conftest import DATADIR
+
+# In this arborescence, we override in the local conftest.py module the
+# "datadir" fixture to specify where to retrieve the data files from.
+
+
+def test_requests_mock_datadir_with_datadir_fixture_override(
+        requests_mock_datadir):
+    """Override datadir fixture should retrieve data from elsewhere
+
+    """
+    response = requests.get('https://example.com/file.json')
+    assert response.ok
+    assert response.json() == {'welcome': 'you'}
+
+
+def test_data_dir_override(datadir):
+    assert datadir == DATADIR
diff --git a/swh/core/tests/test_pytest_plugin.py b/swh/core/tests/test_pytest_plugin.py
new file mode 100644
--- /dev/null
+++ b/swh/core/tests/test_pytest_plugin.py
@@ -0,0 +1,90 @@
+# 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 requests
+
+from os import path
+
+from pytest_swh_core import requests_mock_datadir_factory
+
+
+def test_get_response_cb_with_visits_nominal(requests_mock_datadir_visits):
+    response = requests.get('https://example.com/file.json')
+    assert response.ok
+    assert response.json() == {'hello': 'you'}
+
+    response = requests.get('https://example.com/file.json')
+    assert response.ok
+    assert response.json() == {'hello': 'world'}
+
+    response = requests.get('https://example.com/file.json')
+    assert not response.ok
+    assert response.status_code == 404
+
+
+def test_get_response_cb_with_visits(requests_mock_datadir_visits):
+    response = requests.get('https://example.com/file.json')
+    assert response.ok
+    assert response.json() == {'hello': 'you'}
+
+    response = requests.get('https://example.com/other.json')
+    assert response.ok
+    assert response.json() == "foobar"
+
+    response = requests.get('https://example.com/file.json')
+    assert response.ok
+    assert response.json() == {'hello': 'world'}
+
+    response = requests.get('https://example.com/other.json')
+    assert not response.ok
+    assert response.status_code == 404
+
+    response = requests.get('https://example.com/file.json')
+    assert not response.ok
+    assert response.status_code == 404
+
+
+def test_get_response_cb_no_visit(requests_mock_datadir):
+    response = requests.get('https://example.com/file.json')
+    assert response.ok
+    assert response.json() == {'hello': 'you'}
+
+    response = requests.get('https://example.com/file.json')
+    assert response.ok
+    assert response.json() == {'hello': 'you'}
+
+
+requests_mock_datadir_ignore = requests_mock_datadir_factory(
+    ignore_urls=['https://example.com/file.json'],
+    has_multi_visit=False,
+)
+
+
+def test_get_response_cb_ignore_url(requests_mock_datadir_ignore):
+    response = requests.get('https://example.com/file.json')
+    assert not response.ok
+    assert response.status_code == 404
+
+
+requests_mock_datadir_ignore_and_visit = requests_mock_datadir_factory(
+    ignore_urls=['https://example.com/file.json'],
+    has_multi_visit=True,
+)
+
+
+def test_get_response_cb_ignore_url_with_visit(
+        requests_mock_datadir_ignore_and_visit):
+    response = requests.get('https://example.com/file.json')
+    assert not response.ok
+    assert response.status_code == 404
+
+    response = requests.get('https://example.com/file.json')
+    assert not response.ok
+    assert response.status_code == 404
+
+
+def test_data_dir(datadir):
+    expected_datadir = path.join(path.abspath(path.dirname(__file__)), 'data')
+    assert datadir == expected_datadir