D.C. Code § 14-301: Parties and other interested persons generally.

Except as otherwise provided by law, a person is not incompetent to testify in a civil action or proceeding by reason of his being a party thereto or interested in the result thereof. If otherwise competent to testify, he is competent to give evidence on his own behalf and competent and compellable to give evidence on behalf of any other party to the action or proceeding.