diff --git a/multiauthenticator/tests/test_multiauthenticator.py b/multiauthenticator/tests/test_multiauthenticator.py
index 83e28de..5ec313a 100644
--- a/multiauthenticator/tests/test_multiauthenticator.py
+++ b/multiauthenticator/tests/test_multiauthenticator.py
@@ -4,6 +4,7 @@
 """Test module for the MultiAuthenticator class"""
 import pytest
 
+from jupyterhub.auth import DummyAuthenticator
 from jupyterhub.auth import PAMAuthenticator
 from oauthenticator.github import GitHubOAuthenticator
 from oauthenticator.gitlab import GitLabOAuthenticator
@@ -205,8 +206,28 @@ def test_username_prefix():
 
     multi_authenticator = MultiAuthenticator()
     assert len(multi_authenticator._authenticators) == 2
-    assert multi_authenticator._authenticators[0].username_prefix == "GitLab:"
-    assert multi_authenticator._authenticators[1].username_prefix == "PAM:"
+    assert (
+        multi_authenticator._authenticators[0].username_prefix
+        == f"GitLab{PREFIX_SEPARATOR}"
+    )
+    assert (
+        multi_authenticator._authenticators[1].username_prefix
+        == f"PAM{PREFIX_SEPARATOR}"
+    )
+
+
+@pytest.mark.asyncio
+async def test_authenticated_username_prefix():
+    MultiAuthenticator.authenticators = [
+        (DummyAuthenticator, "/pam", {"service_name": "Dummy"}),
+    ]
+
+    multi_authenticator = MultiAuthenticator()
+    assert len(multi_authenticator._authenticators) == 1
+    username = await multi_authenticator._authenticators[0].authenticate(
+        None, {"username": "test"}
+    )
+    assert username == f"Dummy{PREFIX_SEPARATOR}test"
 
 
 def test_username_prefix_checks():
diff --git a/pyproject.toml b/pyproject.toml
index 249b890..86542b7 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -28,7 +28,7 @@ dependencies = [
 ]
 
 [project.optional-dependencies]
-test = ["pytest", "pytest-cov"]
+test = ["pytest", "pytest-cov", "pytest-asyncio"]
 dev = ["pre-commit", "jupyterhub-multiauthenticator[test]"]
 
 [tool.setuptools]