diff --git a/swh/scheduler/tests/updater/conftest.py b/swh/scheduler/tests/updater/conftest.py
new file mode 100644
--- /dev/null
+++ b/swh/scheduler/tests/updater/conftest.py
@@ -0,0 +1,33 @@
+import pytest
+import glob
+import os
+
+from swh.core.utils import numfile_sortkey as sortkey
+from swh.scheduler.updater.backend import SchedulerUpdaterBackend
+from swh.scheduler.tests import SQL_DIR
+import swh.scheduler.tests.conftest  # noqa
+
+
+DUMP_FILES = os.path.join(SQL_DIR, 'updater', '*.sql')
+
+
+@pytest.fixture
+def swh_scheduler_updater(request, postgresql_proc, postgresql):
+    config = {
+        'db': 'postgresql://{user}@{host}:{port}/{dbname}'.format(
+            host=postgresql_proc.host,
+            port=postgresql_proc.port,
+            user='postgres',
+            dbname='tests')
+    }
+
+    all_dump_files = sorted(glob.glob(DUMP_FILES), key=sortkey)
+
+    cursor = postgresql.cursor()
+    for fname in all_dump_files:
+        with open(fname) as fobj:
+            cursor.execute(fobj.read())
+    postgresql.commit()
+
+    backend = SchedulerUpdaterBackend(**config)
+    return backend
diff --git a/swh/scheduler/tests/updater/test_backend.py b/swh/scheduler/tests/updater/test_backend.py
--- a/swh/scheduler/tests/updater/test_backend.py
+++ b/swh/scheduler/tests/updater/test_backend.py
@@ -3,60 +3,34 @@
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
-import os
-import unittest
-
-from arrow import utcnow
 from hypothesis import given
 from hypothesis.strategies import sets
-import pytest
 
-from swh.core.tests.db_testing import SingleDbTestFixture
-from swh.scheduler.tests import SQL_DIR
-from swh.scheduler.updater.backend import SchedulerUpdaterBackend
 from swh.scheduler.updater.events import SWHEvent
 
 from . import from_regex
 
 
-@pytest.mark.db
-class SchedulerUpdaterBackendTest(SingleDbTestFixture, unittest.TestCase):
-    TEST_DB_NAME = 'softwareheritage-scheduler-updater-test'
-    TEST_DB_DUMP = os.path.join(SQL_DIR, 'updater', '*.sql')
-
-    def setUp(self):
-        super().setUp()
-        config = {
-            'db': 'dbname=' + self.TEST_DB_NAME,
-            'cache_read_limit': 1000,
-        }
-        self.backend = SchedulerUpdaterBackend(**config)
-
-    def _empty_tables(self):
-        self.cursor.execute(
-            """SELECT table_name FROM information_schema.tables
-               WHERE table_schema = %s""", ('public', ))
-        tables = set(table for (table,) in self.cursor.fetchall())
-        for table in tables:
-            self.cursor.execute('truncate table %s cascade' % table)
-        self.conn.commit()
-
-    def tearDown(self):
-        self._empty_tables()
-        super().tearDown()
-
-    @given(sets(
-        from_regex(
-            r'^https://somewhere[.]org/[a-z0-9]{5,7}/[a-z0-9]{3,10}$'),
-        min_size=10, max_size=15))
-    def test_cache_read(self, urls):
-        def gen_events(urls):
-            for url in urls:
-                yield SWHEvent({
-                    'url': url,
-                    'type': 'create',
-                    'origin_type': 'git',
-                })
-        self.backend.cache_put(gen_events(urls))
-        r = self.backend.cache_read(timestamp=utcnow())
-        self.assertNotEqual(r, [])
+@given(urls=sets(
+    from_regex(
+        r'^https://somewhere[.]org/[a-z0-9]{5,7}/[a-z0-9]{3,10}$'),
+    min_size=10, max_size=15))
+def test_cache_read(urls, swh_scheduler_updater):
+    # beware that the fixture is only called once for all the tests
+    # generated by hypothesis, so the db is not cleared between calls.
+    # see the end of
+    #   https://hypothesis.works/articles/hypothesis-pytest-fixtures/
+    def gen_events(urls):
+        for url in urls:
+            yield SWHEvent({
+                'url': url,
+                'type': 'create',
+                'origin_type': 'git',
+            })
+    known_urls = set(e['url'] for e in
+                     swh_scheduler_updater.cache_read(limit=1000000))
+    swh_scheduler_updater.cache_put(gen_events(urls))
+    new_urls = {u.strip() for u in urls} - known_urls
+    all_urls = set(e['url'] for e in
+                   swh_scheduler_updater.cache_read(limit=1000000))
+    assert (all_urls - known_urls) == new_urls
diff --git a/swh/scheduler/updater/backend.py b/swh/scheduler/updater/backend.py
--- a/swh/scheduler/updater/backend.py
+++ b/swh/scheduler/updater/backend.py
@@ -47,16 +47,6 @@
         """Write new events in the backend.
 
         """
-        if timestamp is None:
-            timestamp = utcnow()
-
-        def prepare_events(events):
-            for e in events:
-                event = e.get()
-                seen = event['last_seen']
-                if seen is None:
-                    event['last_seen'] = timestamp
-                yield event
         cur.execute('select swh_mktemp_cache()')
         db.copy_to(prepare_events(events, timestamp),
                    'tmp_cache', self.cache_put_keys, cur=cur)
@@ -69,6 +59,9 @@
     def cache_read(self, timestamp=None, limit=None, db=None, cur=None):
         """Read events from the cache prior to timestamp.
 
+        Note that limit=None does not meas 'no limit' but use the default
+        limit.
+
         """
         if not timestamp:
             timestamp = utcnow()
@@ -91,3 +84,28 @@
         q = 'delete from cache where url in (%s)' % (
             ', '.join(("'%s'" % e for e in entries)), )
         cur.execute(q)
+
+
+def prepare_events(events, timestamp=None):
+    if timestamp is None:
+        timestamp = utcnow()
+    outevents = []
+    urls = []
+    for e in events:
+        event = e.get()
+        url = event['url'].strip()
+        if event['last_seen'] is None:
+            event['last_seen'] = timestamp
+        event['url'] = url
+
+        if url in urls:
+            idx = urls.index(url)
+            urls.append(urls.pop(idx))
+            pevent = outevents.pop(idx)
+            event['cnt'] += pevent['cnt']
+            event['last_seen'] = max(
+                event['last_seen'], pevent['last_seen'])
+        else:
+            urls.append(url)
+        outevents.append(event)
+    return outevents