Let me explain. Our present Bible is divided into two parts, the Hebrew Scriptures, called the Old Testament, and the Greek Scriptures, called the New Testament. In another way, though, it is quite misleading. We need to remember that the text of the Bible itself does not create these classifications. Whatever the old and new covenants are, the Bible's teaching does not identify them with the Old and New Testaments, which are rather arbitrary divisions in the Bible's layout.
People rightly equate testament with covenant.
They think that the Old Testament is about old covenant religion, while the New Testament is about new covenant religion. In other words, they have allowed extra-Biblical designations to determine the meaning of these expressions. When we see what the Bible actually teaches, we must come to a radically different conclusion. In a number of places, the Old Testament speaks of the new covenant. If we did not know the rest of the Bible, we may get the idea that this is something entirely new.