to know what was in your heart: God already knew the deepest thoughts of the Israelites (Psalms 51:6; 139:1, 4, 23). He did not need to learn new information. Instead, he wanted their true character to be shown by their actions.
in order to know … whether or not: The Old Testament often describes God in human ways. This is called anthropomorphism (speaking about God as if he has human qualities) and anthropopathism (speaking about God as if he has human emotions). These ways of speaking help people understand God better.
However, God is not limited like humans. He is not limited in knowledge, power, or greatness. In this verse, God is described as if he needed to learn the future. But other passages teach that God knows everything. God knows the past, present, and future (Psalm 139:1–18; Hebrews 4:13).