Add missing library os.

workflow/tests/test_pool_and_psuedoreplicate.py

@@ -3,6 +3,7 @@
 import pytest
 import pandas as pd
 from io import StringIO
+import os
 import pool_and_psuedoreplicate
 
 test_output_path = os.path.dirname(os.path.abspath(__file__)) + \