diff --git a/conftest.py b/conftest.py
new file mode 100644
--- /dev/null
+++ b/conftest.py
@@ -0,0 +1 @@
+pytest_plugins = ["swh.storage.pytest_plugin"]
diff --git a/mypy.ini b/mypy.ini
--- a/mypy.ini
+++ b/mypy.ini
@@ -11,5 +11,8 @@
 [mypy-pytest.*]
 ignore_missing_imports = True
 
+[mypy-psycopg2.*]
+ignore_missing_imports = True
+
 # [mypy-add_your_lib_here.*]
 # ignore_missing_imports = True
diff --git a/requirements-swh.txt b/requirements-swh.txt
--- a/requirements-swh.txt
+++ b/requirements-swh.txt
@@ -1,2 +1,4 @@
 # Add here internal Software Heritage dependencies, one per line.
 swh.core[http] >= 0.3
+swh.model >= 0.9.0
+swh.storage >= 0.11.1
diff --git a/requirements.txt b/requirements.txt
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +0,0 @@
-# Add here external Python modules dependencies, one per line. Module names
-# should match https://pypi.python.org/pypi names. For the full spec or
-# dependency lines, see https://pip.readthedocs.org/en/1.1/requirements.html
-
diff --git a/swh/clearlydefined/mapping_utils.py b/swh/clearlydefined/mapping_utils.py
new file mode 100644
--- /dev/null
+++ b/swh/clearlydefined/mapping_utils.py
@@ -0,0 +1,29 @@
+# Copyright (C) 2017-2021  The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU Affero General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+from typing import Optional
+
+from swh.model.hashutil import hash_to_bytes
+from swh.model.hashutil import hash_to_hex
+import psycopg2
+
+
+def map_sha1_with_swhid(sha1: str, dsn: str) -> Optional[str]:
+    """
+    Take sha1 and dsn as input and give the corresponding
+    swhID for that sha1
+    """
+    if not sha1:
+        return None
+    read_connection = psycopg2.connect(dsn=dsn)
+    cur = read_connection.cursor()
+    sha1 = hash_to_bytes(sha1)
+    cur.execute("SELECT sha1_git FROM content where sha1= %s;", (sha1,))
+    sha1_git_tuple_data = cur.fetchall()
+    if len(sha1_git_tuple_data) == 0:
+        return None
+    sha1_git = hash_to_hex(sha1_git_tuple_data[0][0])
+    swh_id = "swh:1:cnt:{sha1_git}".format(sha1_git=sha1_git)
+    return swh_id
diff --git a/swh/clearlydefined/tests/test_mapping.py b/swh/clearlydefined/tests/test_mapping.py
new file mode 100644
--- /dev/null
+++ b/swh/clearlydefined/tests/test_mapping.py
@@ -0,0 +1,72 @@
+# Copyright (C) 2017-2021  The Software Heritage developers
+# See the AUTHORS file at the top-level directory of this distribution
+# License: GNU Affero General Public License version 3, or any later version
+# See top-level LICENSE file for more information
+
+from swh.clearlydefined.mapping_utils import map_sha1_with_swhid
+import psycopg2
+
+
+def add_data(dsn: str):
+    write_connection = psycopg2.connect(dsn=dsn)
+    cur = write_connection.cursor()
+    data = [
+        {
+            "sha1": "\\xa6628c8a4fbc08c29b8472e2222975e5b9918131",
+            "sha1_git": "\\xe103b11cbfecbc116dacbb1f9ab2a02176092a32",
+            "sha256": (
+                "\\x6ac599151a7aaa8ca5d38dc5bb61b49193a3cadc1ed33de5a57e4d1ecc53c846"
+            ),
+            "blake2s256": (
+                "\\xc509b320abede3580bb1de75a0efa09ba7416db9c8de845a4e1b4317c0b8a8d9"
+            ),
+            "length": 717,
+        },
+        {
+            "sha1": "\\xd1ece3dbe3e78a6648f37206f996e202acb3926b",
+            "sha1_git": "\\x095b80e14c3ea6254f57e94761f2313e32b1d58a",
+            "sha256": (
+                "\\x2a24791d738e4380d55e1c990dd0bd2bcdc98240d9a25c488804abfd814b8c96"
+            ),
+            "blake2s256": (
+                "\\xa18463fe94e1b4ee191815c2fa48948c44ffbdffcda49fad6591ac4c93f19aef"
+            ),
+            "length": 3138,
+        },
+    ]
+    for row in data:
+        cur.execute(
+            "INSERT INTO content (sha1, sha1_git, sha256, blake2s256, length) VALUES \
+                (%s,%s,%s,%s,%s);",
+            (
+                row["sha1"],
+                row["sha1_git"],
+                row["sha256"],
+                row["blake2s256"],
+                row["length"],
+            ),
+        )
+        write_connection.commit()
+
+
+def test_mapping(swh_storage_backend_config):
+    dsn = swh_storage_backend_config["db"]
+    add_data(dsn=dsn)
+    sha1 = "a6628c8a4fbc08c29b8472e2222975e5b9918131"
+    assert "swh:1:cnt:e103b11cbfecbc116dacbb1f9ab2a02176092a32" == map_sha1_with_swhid(
+        sha1=sha1, dsn=dsn
+    )
+
+
+def test_mapping_with_empty_sha1(swh_storage_backend_config):
+    dsn = swh_storage_backend_config["db"]
+    add_data(dsn=dsn)
+    sha1 = ""
+    assert map_sha1_with_swhid(sha1=sha1, dsn=dsn) is None
+
+
+def test_mapping_with_wrong_sha1(swh_storage_backend_config):
+    dsn = swh_storage_backend_config["db"]
+    add_data(dsn=dsn)
+    sha1 = "6ac599151a7aaa8ca5d38dc5bb61b49193a3cadc1ed33de5a57e4d1ecc53c846"
+    assert map_sha1_with_swhid(sha1=sha1, dsn=dsn) is None
diff --git a/swh/clearlydefined/tests/test_nothing.py b/swh/clearlydefined/tests/test_nothing.py
deleted file mode 100644
--- a/swh/clearlydefined/tests/test_nothing.py
+++ /dev/null
@@ -1,3 +0,0 @@
-def test_nothing():
-    # Placeholder; remove this when we add actual tests
-    pass