What is Assertory Covenant?

Legal Definition
One by which the covenantor affirms that a certain fact is in a particular way, as that the grantor of land is lawfully seised; that it is clear of encumbrances, and the like. If the assertion is false, these covenants are broken the moment that the instrument is signed. See 11 S. & R. 109, 112.
-- Bouviers Law Dictionary
Legal Definition
One which affirms that a particular state of facts exists; an affirming promise under seal.—Black.
-- Ballentine's Law Dictionary
Legal Definition
One which affirms that a particular state of facts exists ; an affirming promise under scab
-- Black's Law Dictionary