diff --git a/documentai/snippets/noxfile.py b/documentai/snippets/noxfile.py
index f2320ea0001c..be1a3f251496 100644
--- a/documentai/snippets/noxfile.py
+++ b/documentai/snippets/noxfile.py
@@ -174,10 +174,16 @@ def _session_tests(
 ) -> None:
     """Runs py.test for a particular project."""
     if os.path.exists("requirements.txt"):
-        session.install("-r", "requirements.txt")
+        if os.path.exists("constraints.txt"):
+            session.install("-r", "requirements.txt", "-c", "constraints.txt")
+        else:
+            session.install("-r", "requirements.txt")
 
     if os.path.exists("requirements-test.txt"):
-        session.install("-r", "requirements-test.txt")
+        if os.path.exists("constraints-test.txt"):
+            session.install("-r", "requirements-test.txt", "-c", "constraints-test.txt")
+        else:
+            session.install("-r", "requirements-test.txt")
 
     if INSTALL_LIBRARY_FROM_SOURCE:
         session.install("-e", _get_repo_root())