Cathie Wood’s investment firm, known for investing in companies that are shaking up their industries, is testing a portfolio that would let her bet against the corporate victims of that disruption.

Wood, a widely followed stock picker, founded and runs the asset-management firm ARK Invest. ARK currently offers six actively managed exchange-traded funds, but none have the capability to short stocks––borrowing shares and selling them later in a bet that prices would drop.

The…