In his farewell, Joshua told Israel how many of the LORD's good promises to them had failed?

Answer: Not one

Joshua said, "Not one of the good promises the LORD your God made to you has failed. Everything was fulfilled for you."

“Now behold, today I am going the way of all the earth, and you know with all your heart and soul that not one of the good promises the LORD your God made to you has failed. Everything was fulfilled for you; not one promise has failed.”— Joshua 23:14 (BSB)