old_contents: import os
  
  from sqlalchemy.ext.automap import automap_base
  from sqlalchemy.orm import sessionmaker
  from sqlalchemy import create_engine
  from sqlalchemy.orm.scoping import scoped_session
  
  DB_URL = os.environ['DB_URL']
  Base = automap_base()
  engine = create_engine(DB_URL)
  Base.prepare(engine, reflect=True)
  
  session_factory  = sessionmaker(bind=engine, expire_on_commit=False)
  Session = scoped_session(session_factory)
new_contents: import os
  
  from sqlalchemy.ext.automap import automap_base
  from sqlalchemy.orm import sessionmaker
  from sqlalchemy import create_engine
  from sqlalchemy.orm.scoping import scoped_session
  
  DB_URL = os.environ['DB_URL']
  
  if not DB_URL:
      raise ValueError("DB_URL not present in the environment")
  
  Base = automap_base()
  engine = create_engine(DB_URL)
  Base.prepare(engine, reflect=True)
  
  session_factory  = sessionmaker(bind=engine, expire_on_commit=False)
  Session = scoped_session(session_factory)
subject: Test for DB_URL being present in environment.