diff --git a/requirements.txt b/requirements.txt
--- a/requirements.txt
+++ b/requirements.txt
@@ -4,6 +4,7 @@
 click
 iso8601
 methodtools
+mongomock
 pymongo
 PyYAML
 types-click
diff --git a/swh/provenance/__init__.py b/swh/provenance/__init__.py
--- a/swh/provenance/__init__.py
+++ b/swh/provenance/__init__.py
@@ -72,8 +72,6 @@
         :cls:`ValueError` if passed an unknown archive class.
     """
     if cls in ["local", "postgresql"]:
-        from swh.core.db import BaseDb
-
         from .postgresql.provenance import ProvenanceStoragePostgreSql
 
         if cls == "local":
@@ -83,18 +81,16 @@
                 DeprecationWarning,
             )
 
-        conn = BaseDb.connect(**kwargs["db"]).conn
         raise_on_commit = kwargs.get("raise_on_commit", False)
-        return ProvenanceStoragePostgreSql(conn, raise_on_commit)
+        return ProvenanceStoragePostgreSql(
+            raise_on_commit=raise_on_commit, **kwargs["db"]
+        )
 
     elif cls == "mongodb":
-        from pymongo import MongoClient
-
         from .mongo.backend import ProvenanceStorageMongoDb
 
-        dbname = kwargs["db"].pop("dbname")
-        db = MongoClient(**kwargs["db"]).get_database(dbname)
-        return ProvenanceStorageMongoDb(db)
+        engine = kwargs.get("engine", "pymongo")
+        return ProvenanceStorageMongoDb(engine=engine, **kwargs["db"])
 
     elif cls in ["remote", "rpcapi"]:
         from .api.client import ProvenanceStorageRPCClient
diff --git a/swh/provenance/api/server.py b/swh/provenance/api/server.py
--- a/swh/provenance/api/server.py
+++ b/swh/provenance/api/server.py
@@ -23,6 +23,7 @@
     global storage
     if storage is None:
         storage = get_provenance_storage(**app.config["provenance"]["storage"])
+        storage.open()  # XXX: nobody is closing this storage!
     return storage
 
 
diff --git a/swh/provenance/cli.py b/swh/provenance/cli.py
--- a/swh/provenance/cli.py
+++ b/swh/provenance/cli.py
@@ -152,6 +152,7 @@
     revisions_provider = generate_revision_tuples(filename)
     revisions = CSVRevisionIterator(revisions_provider, limit=limit)
 
+    provenance.open()
     for revision in revisions:
         revision_add(
             provenance,
@@ -161,6 +162,7 @@
             lower=reuse,
             mindepth=min_depth,
         )
+    provenance.close()
 
 
 def generate_revision_tuples(
@@ -190,8 +192,10 @@
     origins_provider = generate_origin_tuples(filename)
     origins = CSVOriginIterator(origins_provider, limit=limit)
 
+    provenance.open()
     for origin in origins:
         origin_add(provenance, archive, [origin])
+    provenance.close()
 
 
 def generate_origin_tuples(filename: str) -> Generator[Tuple[str, bytes], None, None]:
@@ -209,6 +213,8 @@
     from . import get_provenance
 
     provenance = get_provenance(**ctx.obj["config"]["provenance"]["storage"])
+
+    provenance.open()
     occur = provenance.content_find_first(hash_to_bytes(swhid))
     if occur is not None:
         print(
@@ -220,6 +226,7 @@
         )
     else:
         print(f"Cannot find a content with the id {swhid}")
+    provenance.close()
 
 
 @cli.command(name="find-all")
@@ -231,6 +238,8 @@
     from . import get_provenance
 
     provenance = get_provenance(**ctx.obj["config"]["provenance"]["storage"])
+
+    provenance.open()
     for occur in provenance.content_find_all(hash_to_bytes(swhid), limit=limit):
         print(
             f"swh:1:cnt:{hash_to_hex(occur.content)}, "
@@ -239,3 +248,4 @@
             f"{occur.origin}, "
             f"{os.fsdecode(occur.path)}"
         )
+    provenance.close()
diff --git a/swh/provenance/interface.py b/swh/provenance/interface.py
--- a/swh/provenance/interface.py
+++ b/swh/provenance/interface.py
@@ -65,6 +65,11 @@
 
 @runtime_checkable
 class ProvenanceStorageInterface(Protocol):
+    @remote_api_endpoint("close")
+    def close(self) -> None:
+        """Close connection to the storage and release resources."""
+        ...
+
     @remote_api_endpoint("content_add")
     def content_add(
         self, cnts: Union[Iterable[Sha1Git], Dict[Sha1Git, Optional[datetime]]]
@@ -129,6 +134,11 @@
         This method is used only in tests."""
         ...
 
+    @remote_api_endpoint("open")
+    def open(self) -> None:
+        """Open connection to the storage and allocate necessary resources."""
+        ...
+
     @remote_api_endpoint("origin_add")
     def origin_add(self, orgs: Dict[Sha1Git, str]) -> bool:
         """Add origins identified by sha1 ids, with their corresponding url (as paired
@@ -198,6 +208,10 @@
 class ProvenanceInterface(Protocol):
     storage: ProvenanceStorageInterface
 
+    def close(self) -> None:
+        """Close connection to the underlying `storage` and release resources."""
+        ...
+
     def flush(self) -> None:
         """Flush internal cache to the underlying `storage`."""
         ...
@@ -279,6 +293,12 @@
         """
         ...
 
+    def open(self) -> None:
+        """Open connection to the underlying `storage` and allocate necessary
+        resources.
+        """
+        ...
+
     def origin_add(self, origin: OriginEntry) -> None:
         """Add `origin` to the provenance model."""
         ...
diff --git a/swh/provenance/mongo/backend.py b/swh/provenance/mongo/backend.py
--- a/swh/provenance/mongo/backend.py
+++ b/swh/provenance/mongo/backend.py
@@ -8,7 +8,8 @@
 from typing import Any, Dict, Generator, Iterable, List, Optional, Set, Union
 
 from bson import ObjectId
-import pymongo.database
+import mongomock
+import pymongo
 
 from swh.model.model import Sha1Git
 
@@ -22,8 +23,13 @@
 
 
 class ProvenanceStorageMongoDb:
-    def __init__(self, db: pymongo.database.Database):
-        self.db = db
+    def __init__(self, engine: str, **kwargs):
+        self.engine = engine
+        self.dbname = kwargs.pop("dbname")
+        self.conn_args = kwargs
+
+    def close(self) -> None:
+        self.db.client.close()
 
     def content_add(
         self, cnts: Union[Iterable[Sha1Git], Dict[Sha1Git, Optional[datetime]]]
@@ -203,6 +209,13 @@
             paths.extend(value for _, value in each_dir["revision"].items())
         return set(sum(paths, []))
 
+    def open(self) -> None:
+        if self.engine == "mongomock":
+            self.db = mongomock.MongoClient(**self.conn_args).get_database(self.dbname)
+        else:
+            # assume real MongoDB server by default
+            self.db = pymongo.MongoClient(**self.conn_args).get_database(self.dbname)
+
     def origin_add(self, orgs: Dict[Sha1Git, str]) -> bool:
         existing = {
             x["sha1"]: x
diff --git a/swh/provenance/postgresql/provenance.py b/swh/provenance/postgresql/provenance.py
--- a/swh/provenance/postgresql/provenance.py
+++ b/swh/provenance/postgresql/provenance.py
@@ -28,13 +28,8 @@
 
 
 class ProvenanceStoragePostgreSql:
-    def __init__(
-        self, conn: psycopg2.extensions.connection, raise_on_commit: bool = False
-    ) -> None:
-        BaseDb.adapt_conn(conn)
-        self.conn = conn
-        with self.transaction() as cursor:
-            cursor.execute("SET timezone TO 'UTC'")
+    def __init__(self, raise_on_commit: bool = False, **kwargs) -> None:
+        self.conn_args = kwargs
         self._flavor: Optional[str] = None
         self.raise_on_commit = raise_on_commit
 
@@ -60,6 +55,9 @@
     def denormalized(self) -> bool:
         return "denormalized" in self.flavor
 
+    def close(self) -> None:
+        self.conn.close()
+
     def content_add(
         self, cnts: Union[Iterable[Sha1Git], Dict[Sha1Git, Optional[datetime]]]
     ) -> bool:
@@ -140,6 +138,12 @@
                 raise
         return False
 
+    def open(self) -> None:
+        self.conn = BaseDb.connect(**self.conn_args).conn
+        BaseDb.adapt_conn(self.conn)
+        with self.transaction() as cursor:
+            cursor.execute("SET timezone TO 'UTC'")
+
     def origin_get(self, ids: Iterable[Sha1Git]) -> Dict[Sha1Git, str]:
         urls: Dict[Sha1Git, str] = {}
         sha1s = tuple(ids)
diff --git a/swh/provenance/provenance.py b/swh/provenance/provenance.py
--- a/swh/provenance/provenance.py
+++ b/swh/provenance/provenance.py
@@ -77,6 +77,9 @@
     def clear_caches(self) -> None:
         self.cache = new_cache()
 
+    def close(self) -> None:
+        self.storage.close()
+
     def flush(self) -> None:
         # Revision-content layer insertions ############################################
 
@@ -336,6 +339,9 @@
                 dates[sha1] = date
         return dates
 
+    def open(self) -> None:
+        self.storage.open()
+
     def origin_add(self, origin: OriginEntry) -> None:
         self.cache["origin"]["data"][origin.id] = origin.url
         self.cache["origin"]["added"].add(origin.id)
diff --git a/swh/provenance/tests/conftest.py b/swh/provenance/tests/conftest.py
--- a/swh/provenance/tests/conftest.py
+++ b/swh/provenance/tests/conftest.py
@@ -5,12 +5,12 @@
 
 from datetime import datetime, timedelta, timezone
 from os import path
-from typing import Any, Dict, Iterable, Iterator
+from typing import Any, Dict, Generator, Iterable, Iterator
 
 from _pytest.fixtures import SubRequest
+import mongomock.database
 import msgpack
 import psycopg2.extensions
-import pymongo.database
 import pytest
 from pytest_postgresql.factories import postgresql
 
@@ -55,7 +55,9 @@
     server.storage = get_provenance_storage(
         cls="postgresql", db=provenance_postgresqldb
     )
+    server.storage.open()
     yield server.app
+    server.storage.close()
 
 
 # the RPCClient class used as client used in these tests
@@ -68,25 +70,38 @@
 def provenance_storage(
     request: SubRequest,
     provenance_postgresqldb: Dict[str, str],
-    mongodb: pymongo.database.Database,
+    mongodb: mongomock.database.Database,
     swh_rpc_client: ProvenanceStorageRPCClient,
-) -> ProvenanceStorageInterface:
+) -> Generator[ProvenanceStorageInterface, None, None]:
     """Return a working and initialized ProvenanceStorageInterface object"""
 
     if request.param == "rpcapi":
         assert isinstance(swh_rpc_client, ProvenanceStorageInterface)
-        return swh_rpc_client
+        swh_rpc_client.open()
+        yield swh_rpc_client
+        swh_rpc_client.close()
 
     elif request.param == "mongodb":
-        from swh.provenance.mongo.backend import ProvenanceStorageMongoDb
-
-        return ProvenanceStorageMongoDb(mongodb)
+        mongodb_params = {
+            "host": mongodb.client.address[0],
+            "port": mongodb.client.address[1],
+            "dbname": mongodb.name,
+        }
+        mongodb_storage = get_provenance_storage(
+            cls=request.param, db=mongodb_params, engine="mongomock"
+        )
+        mongodb_storage.open()
+        yield mongodb_storage
+        mongodb_storage.close()
 
     else:
         # in test sessions, we DO want to raise any exception occurring at commit time
-        return get_provenance_storage(
+        storage = get_provenance_storage(
             cls=request.param, db=provenance_postgresqldb, raise_on_commit=True
         )
+        storage.open()
+        yield storage
+        storage.close()
 
 
 provenance_postgresql = postgresql("postgresql_proc", dbname="provenance_tests")
@@ -95,7 +110,7 @@
 @pytest.fixture
 def provenance(
     provenance_postgresql: psycopg2.extensions.connection,
-) -> ProvenanceInterface:
+) -> Generator[ProvenanceInterface, None, None]:
     """Return a working and initialized ProvenanceInterface object"""
 
     from swh.core.cli.db import populate_database_for_package
@@ -104,11 +119,14 @@
         "swh.provenance", provenance_postgresql.dsn, flavor="with-path"
     )
     # in test sessions, we DO want to raise any exception occurring at commit time
-    return get_provenance(
+    provenance = get_provenance(
         cls="postgresql",
         db=provenance_postgresql.get_dsn_parameters(),
         raise_on_commit=True,
     )
+    provenance.open()
+    yield provenance
+    provenance.close()
 
 
 @pytest.fixture