diff --git a/app/services/user_service.py b/app/services/user_service.py
index 410b807..307db06 100644
--- a/app/services/user_service.py
+++ b/app/services/user_service.py
@@ -16,3 +16,10 @@ def get_user(user_id):
 def delete_user(user_id):
     """user_id로 회원 삭제"""
     pass
+
+
+user_db = {}  # 임시 DB
+
+def get_user_info(user_id: str):
+    """등록된 유저를 user_id로 조회"""
+    return user_db.get(user_id)
\ No newline at end of file
diff --git a/tests/test_service_users.py b/tests/test_service_users.py
index e69de29..f98a8e0 100644
--- a/tests/test_service_users.py
+++ b/tests/test_service_users.py
@@ -0,0 +1,11 @@
+from app.services.user_service import get_user_info
+
+def test_query_nonexistent_user_returns_none():
+    # Given
+    nonexistent_user_id = "ghost_user_999"
+
+    # When
+    result = get_user_info(nonexistent_user_id)
+
+    # Then
+    assert result is None
\ No newline at end of file