RCW 11.12.060: Agreement to convey does not revoke.

A bond, covenant, or agreement made for a valuable consideration by a testator to convey any property, devised or bequeathed in any last will previously made, shall not be deemed a revocation of such previous devise or bequest, but such property shall pass by the devise or bequest, subject to the same remedies on such bond, covenant, or agreement, for specific performance or otherwise, against devisees or legatees, as might be had by law against the heirs of the testator or his or her next of kin, if the same had descended to him or her.