diff --git a/tests/routers/openml/setups_tag_test.py b/tests/routers/openml/setups_tag_test.py
index 44d31f2..05e326a 100644
--- a/tests/routers/openml/setups_tag_test.py
+++ b/tests/routers/openml/setups_tag_test.py
@@ -1,4 +1,3 @@
-import re
 from http import HTTPStatus
 
 import httpx
@@ -6,7 +5,9 @@
 from sqlalchemy import text
 from sqlalchemy.ext.asyncio import AsyncConnection
 
-from tests.users import ApiKey
+from core.errors import SetupNotFoundError, TagAlreadyExistsError
+from routers.openml.setups import tag_setup
+from tests.users import SOME_USER, ApiKey
 
 
 async def test_setup_tag_missing_auth(py_api: httpx.AsyncClient) -> None:
@@ -16,41 +17,68 @@ async def test_setup_tag_missing_auth(py_api: httpx.AsyncClient) -> None:
     assert response.json()["detail"] == "Authentication failed"
 
 
-async def test_setup_tag_unknown_setup(py_api: httpx.AsyncClient) -> None:
+@pytest.mark.mut
+async def test_setup_tag_api_success(
+    py_api: httpx.AsyncClient, expdb_test: AsyncConnection
+) -> None:
+    tag = "setup_tag_via_http"
     response = await py_api.post(
         f"/setup/tag?api_key={ApiKey.SOME_USER}",
-        json={"setup_id": 999999, "tag": "test_tag"},
+        json={"setup_id": 1, "tag": tag},
     )
-    assert response.status_code == HTTPStatus.NOT_FOUND
-    assert re.match(r"Setup \d+ not found.", response.json()["detail"])
+
+    assert response.status_code == HTTPStatus.OK
+    assert response.json()["setup_tag"]["tag"][-1] == tag
+
+    rows = await expdb_test.execute(
+        text("SELECT * FROM setup_tag WHERE id = 1 AND tag = :tag"),
+        parameters={"tag": tag},
+    )
+    assert len(rows.all()) == 1
+
+
+# ── Direct call tests: tag_setup ──
+
+
+async def test_setup_tag_unknown_setup(expdb_test: AsyncConnection) -> None:
+    with pytest.raises(SetupNotFoundError, match=r"Setup \d+ not found."):
+        await tag_setup(
+            setup_id=999999,
+            tag="test_tag",
+            user=SOME_USER,
+            expdb_db=expdb_test,
+        )
 
 
 @pytest.mark.mut
-async def test_setup_tag_already_exists(
-    py_api: httpx.AsyncClient, expdb_test: AsyncConnection
-) -> None:
+async def test_setup_tag_already_exists(expdb_test: AsyncConnection) -> None:
+    tag = "setup_tag_conflict"
     await expdb_test.execute(
-        text("INSERT INTO setup_tag (id, tag, uploader) VALUES (1, 'existing_tag_123', 2);")
+        text("INSERT INTO setup_tag (id, tag, uploader) VALUES (1, :tag, 2);"),
+        parameters={"tag": tag},
     )
-    response = await py_api.post(
-        f"/setup/tag?api_key={ApiKey.SOME_USER}",
-        json={"setup_id": 1, "tag": "existing_tag_123"},
-    )
-    assert response.status_code == HTTPStatus.CONFLICT
-    assert response.json()["detail"] == "Setup 1 already has tag 'existing_tag_123'."
+    with pytest.raises(TagAlreadyExistsError, match=rf"Setup 1 already has tag '{tag}'\."):
+        await tag_setup(
+            setup_id=1,
+            tag=tag,
+            user=SOME_USER,
+            expdb_db=expdb_test,
+        )
 
 
 @pytest.mark.mut
-async def test_setup_tag_success(py_api: httpx.AsyncClient, expdb_test: AsyncConnection) -> None:
-    response = await py_api.post(
-        f"/setup/tag?api_key={ApiKey.SOME_USER}",
-        json={"setup_id": 1, "tag": "my_new_success_tag"},
+async def test_setup_tag_direct_success(expdb_test: AsyncConnection) -> None:
+    tag = "setup_tag_via_direct"
+    result = await tag_setup(
+        setup_id=1,
+        tag=tag,
+        user=SOME_USER,
+        expdb_db=expdb_test,
     )
 
-    assert response.status_code == HTTPStatus.OK
-    assert "my_new_success_tag" in response.json()["setup_tag"]["tag"]
-
+    assert result["setup_tag"]["tag"][-1] == tag
     rows = await expdb_test.execute(
-        text("SELECT * FROM setup_tag WHERE id = 1 AND tag = 'my_new_success_tag'")
+        text("SELECT * FROM setup_tag WHERE id = 1 AND tag = :tag"),
+        parameters={"tag": tag},
     )
     assert len(rows.all()) == 1