diff --git a/swh/loader/package/nixguix/tests/test_nixguix.py b/swh/loader/package/nixguix/tests/test_nixguix.py
--- a/swh/loader/package/nixguix/tests/test_nixguix.py
+++ b/swh/loader/package/nixguix/tests/test_nixguix.py
@@ -15,7 +15,7 @@
 
 from unittest.mock import patch
 
-from swh.model.model import Snapshot, TargetType
+from swh.model.model import Snapshot, SnapshotBranch, TargetType
 from swh.loader.package.archive.loader import ArchiveLoader
 from swh.loader.package.nixguix.loader import (
     NixGuixLoader,
@@ -37,6 +37,21 @@
 sources_url = "https://nix-community.github.io/nixpkgs-swh/sources.json"
 
 
+SNAPSHOT1 = Snapshot(
+    id=hash_to_bytes("0c5881c74283793ebe9a09a105a9381e41380383"),
+    branches={
+        b"evaluation": SnapshotBranch(
+            target=hash_to_bytes("cc4e04c26672dd74e5fd0fecb78b435fb55368f7"),
+            target_type=TargetType.REVISION,
+        ),
+        b"https://github.com/owner-1/repository-1/revision-1.tgz": SnapshotBranch(
+            target=hash_to_bytes("488ad4e7b8e2511258725063cf43a2b897c503b4"),
+            target_type=TargetType.REVISION,
+        ),
+    },
+)
+
+
 def check_snapshot(
     snapshot: Union[Dict[str, Any], Snapshot],
     storage: StorageInterface,
@@ -104,16 +119,16 @@
     assert len(clean["sources"]) == 1
 
 
-def check_snapshot_revisions_ok(snapshot, storage):
+def check_snapshot_revisions_ok(snapshot: Snapshot, storage: StorageInterface):
     """Ensure the snapshot revisions are structurally as expected
 
     """
     revision_ids = []
-    for name, branch in snapshot["branches"].items():
+    for name, branch in snapshot.branches.items():
         if name == b"evaluation":
             continue  # skipping that particular branch
-        if branch["target_type"] == "revision":
-            revision_ids.append(branch["target"])
+        if branch.target_type == TargetType.REVISION:
+            revision_ids.append(branch.target)
 
     revisions = storage.revision_get(revision_ids)
     for rev in revisions:
@@ -180,29 +195,18 @@
     load_status = loader.load()
 
     loader.load()
-    expected_snapshot_id = "0c5881c74283793ebe9a09a105a9381e41380383"
-    assert load_status == {"status": "eventful", "snapshot_id": expected_snapshot_id}
+    assert load_status == {"status": "eventful", "snapshot_id": SNAPSHOT1.id.hex()}
 
     assert_last_visit_matches(
-        loader.storage, sources_url, status="partial", type="nixguix"
+        loader.storage,
+        sources_url,
+        status="partial",
+        type="nixguix",
+        snapshot=SNAPSHOT1.id,
     )
 
-    expected_branches = {
-        b"evaluation": {
-            "target": hash_to_bytes("cc4e04c26672dd74e5fd0fecb78b435fb55368f7"),
-            "target_type": "revision",
-        },
-        b"https://github.com/owner-1/repository-1/revision-1.tgz": {
-            "target": hash_to_bytes("488ad4e7b8e2511258725063cf43a2b897c503b4"),
-            "target_type": "revision",
-        },
-    }
-    expected_snapshot = {
-        "id": hash_to_bytes(expected_snapshot_id),
-        "branches": expected_branches,
-    }
-    snapshot = check_snapshot(expected_snapshot, storage=loader.storage)
-    check_snapshot_revisions_ok(snapshot, loader.storage)
+    check_snapshot(SNAPSHOT1, storage=loader.storage)
+    check_snapshot_revisions_ok(SNAPSHOT1, loader.storage)
 
     urls = [
         m.url
@@ -226,30 +230,18 @@
     """
     loader = NixGuixLoader(sources_url)
     load_status = loader.load()
-    expected_snapshot_id = "0c5881c74283793ebe9a09a105a9381e41380383"
-    assert load_status == {"status": "eventful", "snapshot_id": expected_snapshot_id}
+    assert load_status == {"status": "eventful", "snapshot_id": SNAPSHOT1.id.hex()}
 
     assert_last_visit_matches(
-        loader.storage, sources_url, status="partial", type="nixguix"
+        loader.storage,
+        sources_url,
+        status="partial",
+        type="nixguix",
+        snapshot=SNAPSHOT1.id,
     )
 
-    expected_branches = {
-        b"evaluation": {
-            "target": hash_to_bytes("cc4e04c26672dd74e5fd0fecb78b435fb55368f7"),
-            "target_type": "revision",
-        },
-        b"https://github.com/owner-1/repository-1/revision-1.tgz": {
-            "target": hash_to_bytes("488ad4e7b8e2511258725063cf43a2b897c503b4"),
-            "target_type": "revision",
-        },
-    }
-
-    expected_snapshot = {
-        "id": hash_to_bytes(expected_snapshot_id),
-        "branches": expected_branches,
-    }
-    snapshot = check_snapshot(expected_snapshot, storage=loader.storage)
-    check_snapshot_revisions_ok(snapshot, loader.storage)
+    check_snapshot(SNAPSHOT1, storage=loader.storage)
+    check_snapshot_revisions_ok(SNAPSHOT1, loader.storage)
 
     stats = get_stats(loader.storage)
     assert {
@@ -266,37 +258,43 @@
 
     loader = NixGuixLoader(sources_url)
     load_status = loader.load()
-    expected_snapshot_id = "b0bfa75cbd0cc90aac3b9e95fb0f59c731176d97"
-    assert load_status == {"status": "eventful", "snapshot_id": expected_snapshot_id}
+    expected_snapshot_id_hex = "b0bfa75cbd0cc90aac3b9e95fb0f59c731176d97"
+    expected_snapshot_id = hash_to_bytes(expected_snapshot_id_hex)
+    assert load_status == {
+        "status": "eventful",
+        "snapshot_id": expected_snapshot_id_hex,
+    }
 
     assert_last_visit_matches(
-        loader.storage, sources_url, status="partial", type="nixguix"
+        loader.storage,
+        sources_url,
+        status="partial",
+        type="nixguix",
+        snapshot=expected_snapshot_id,
     )
 
     # This ensures visits are incremental. Indeed, if we request a
     # second time an url, because of the requests_mock_datadir_visits
     # fixture, the file has to end with `_visit1`.
-    expected_branches = {
-        b"evaluation": {
-            "target": hash_to_bytes("602140776b2ce6c9159bcf52ada73a297c063d5e"),
-            "target_type": "revision",
-        },
-        b"https://github.com/owner-1/repository-1/revision-1.tgz": {
-            "target": hash_to_bytes("488ad4e7b8e2511258725063cf43a2b897c503b4"),
-            "target_type": "revision",
-        },
-        b"https://github.com/owner-2/repository-1/revision-1.tgz": {
-            "target": hash_to_bytes("85e0bad74e33e390aaeb74f139853ae3863ee544"),
-            "target_type": "revision",
+    expected_snapshot = Snapshot(
+        id=expected_snapshot_id,
+        branches={
+            b"evaluation": SnapshotBranch(
+                target=hash_to_bytes("602140776b2ce6c9159bcf52ada73a297c063d5e"),
+                target_type=TargetType.REVISION,
+            ),
+            b"https://github.com/owner-1/repository-1/revision-1.tgz": SnapshotBranch(
+                target=hash_to_bytes("488ad4e7b8e2511258725063cf43a2b897c503b4"),
+                target_type=TargetType.REVISION,
+            ),
+            b"https://github.com/owner-2/repository-1/revision-1.tgz": SnapshotBranch(
+                target=hash_to_bytes("85e0bad74e33e390aaeb74f139853ae3863ee544"),
+                target_type=TargetType.REVISION,
+            ),
         },
-    }
-
-    expected_snapshot = {
-        "id": hash_to_bytes(expected_snapshot_id),
-        "branches": expected_branches,
-    }
-    snapshot = check_snapshot(expected_snapshot, storage=loader.storage)
-    check_snapshot_revisions_ok(snapshot, loader.storage)
+    )
+    check_snapshot(expected_snapshot, storage=loader.storage)
+    check_snapshot_revisions_ok(expected_snapshot, loader.storage)
 
     stats = get_stats(loader.storage)
     assert {
@@ -332,27 +330,15 @@
     assert res["status"] == "eventful"
 
     assert_last_visit_matches(
-        loader.storage, sources_url, status="partial", type="nixguix"
+        loader.storage,
+        sources_url,
+        status="partial",
+        type="nixguix",
+        snapshot=SNAPSHOT1.id,
     )
 
-    expected_branches = {
-        b"https://github.com/owner-1/repository-1/revision-1.tgz": {
-            "target": hash_to_bytes("488ad4e7b8e2511258725063cf43a2b897c503b4"),
-            "target_type": "revision",
-        },
-        b"evaluation": {
-            "target": hash_to_bytes("cc4e04c26672dd74e5fd0fecb78b435fb55368f7"),
-            "target_type": "revision",
-        },
-    }
-
-    expected_snapshot = {
-        "id": hash_to_bytes("0c5881c74283793ebe9a09a105a9381e41380383"),
-        "branches": expected_branches,
-    }
-
-    snapshot = check_snapshot(expected_snapshot, storage=loader.storage)
-    check_snapshot_revisions_ok(snapshot, loader.storage)
+    check_snapshot(SNAPSHOT1, storage=loader.storage)
+    check_snapshot_revisions_ok(SNAPSHOT1, loader.storage)
 
 
 def test_eoferror(swh_config, requests_mock_datadir):
@@ -367,19 +353,18 @@
     loader = NixGuixLoader(sources)
     loader.load()
 
-    expected_branches = {
-        b"evaluation": {
-            "target": hash_to_bytes("cc4e04c26672dd74e5fd0fecb78b435fb55368f7"),
-            "target_type": "revision",
+    expected_snapshot = Snapshot(
+        id=hash_to_bytes("4257fa2350168c6bfec726a06452ea27a2c0cb33"),
+        branches={
+            b"evaluation": SnapshotBranch(
+                target=hash_to_bytes("cc4e04c26672dd74e5fd0fecb78b435fb55368f7"),
+                target_type=TargetType.REVISION,
+            ),
         },
-    }
-    expected_snapshot = {
-        "id": hash_to_bytes("4257fa2350168c6bfec726a06452ea27a2c0cb33"),
-        "branches": expected_branches,
-    }
+    )
 
-    snapshot = check_snapshot(expected_snapshot, storage=loader.storage)
-    check_snapshot_revisions_ok(snapshot, loader.storage)
+    check_snapshot(expected_snapshot, storage=loader.storage)
+    check_snapshot_revisions_ok(expected_snapshot, loader.storage)
 
 
 def fake_download(
@@ -409,29 +394,13 @@
     loader = NixGuixLoader(sources_url)
     res = loader.load()
 
-    expected_snapshot_id = "0c5881c74283793ebe9a09a105a9381e41380383"
     assert res == {
         "status": "eventful",
-        "snapshot_id": expected_snapshot_id,
-    }
-
-    expected_branches = {
-        b"https://github.com/owner-1/repository-1/revision-1.tgz": {
-            "target": hash_to_bytes("488ad4e7b8e2511258725063cf43a2b897c503b4"),
-            "target_type": "revision",
-        },
-        b"evaluation": {
-            "target": hash_to_bytes("cc4e04c26672dd74e5fd0fecb78b435fb55368f7"),
-            "target_type": "revision",
-        },
-    }
-    expected_snapshot = {
-        "id": hash_to_bytes(expected_snapshot_id),
-        "branches": expected_branches,
+        "snapshot_id": SNAPSHOT1.id.hex(),
     }
 
-    snapshot = check_snapshot(expected_snapshot, storage=loader.storage)
-    check_snapshot_revisions_ok(snapshot, loader.storage)
+    check_snapshot(SNAPSHOT1, storage=loader.storage)
+    check_snapshot_revisions_ok(SNAPSHOT1, loader.storage)
 
     assert len(mock_download.mock_calls) == 2