🐛(backend) validate user search input data

Only the input data min length was checked. We also have to check the
mex length because the levenshtein dos not accept more than 254
characters and the email field has a max length of 254

src/backend/core/tests/test_api_users.py

@@ -194,18 +194,41 @@ def test_api_users_list_query_short_queries():
     factories.UserFactory(email="john.lennon@example.com")
 
     response = client.get("/api/v1.0/users/?q=jo")
-    assert response.status_code == 200
-    assert response.json() == []
+    assert response.status_code == 400
+    assert response.json() == {
+        "q": ["Ensure this value has at least 5 characters (it has 2)."]
+    }
 
     response = client.get("/api/v1.0/users/?q=john")
-    assert response.status_code == 200
-    assert response.json() == []
+    assert response.status_code == 400
+    assert response.json() == {
+        "q": ["Ensure this value has at least 5 characters (it has 4)."]
+    }
 
     response = client.get("/api/v1.0/users/?q=john.")
     assert response.status_code == 200
     assert len(response.json()) == 2
 
 
+def test_api_users_list_query_long_queries():
+    """
+    Queries longer than 255 characters should return an empty result set.
+    """
+    user = factories.UserFactory(email="paul@example.com")
+    client = APIClient()
+    client.force_login(user)
+
+    factories.UserFactory(email="john.doe@example.com")
+    factories.UserFactory(email="john.lennon@example.com")
+
+    query = "a" * 244
+    response = client.get(f"/api/v1.0/users/?q={query}@example.com")
+    assert response.status_code == 400
+    assert response.json() == {
+        "q": ["Ensure this value has at most 254 characters (it has 256)."]
+    }
+
+
 def test_api_users_list_query_inactive():
     """Inactive users should not be listed."""
     user = factories.UserFactory()