New Revised Standard Version
They were for the testing of Israel, to know whether Israel would obey the commandments of the LORD, which he commanded their ancestors by Moses.

Contemporary English Version
Moses had told the Israelites what the LORD had commanded them to do, and now the LORD was using these nations to find out if Israel would obey.

New American Bible
These served as a test for Israel, to know whether they would obey the commandments the LORD had enjoined on their ancestors through Moses.

Douay-Rheims Bible
And he left them, that he might try Israel by them, whether they would hear the commandments of the Lord, which he had commanded their fathers, by the hand of Moses, or not.

And he left them, that he might try Israel by them, whether they would hear the commandments of the Lord, which he had commanded their fathers, by the hand of Moses, or not.

to prove

Judges 3:1 These are the nations which the Lord left, that by them he might instruct Israel, and all that had not known the wars of the Chanaanites:

Judges 2:22 That through them I may try Israel, whether they will keep the way of the Lord, and walk in it, as their fathers kept it, or not.

Exodus 15:25 But he cried to the Lord, and he shewed him a tree, which when he had cast into the waters, they were turned into sweetness. There he appointed him ordinances, and judgments, and there he proved him,

Deuteronomy 33:8 To Levi also he said: Thy perfection, and thy doctrine be to thy holy man, whom thou hast proved in the temptation, and judged at the waters of contradiction:

1 Corinthians 11:19 For there must be also heresies: that they also, who are approved may be made manifest among you.

2 Thessalonians 2:9-12 Whose coming is according to the working of Satan, in all power and signs and lying wonders: . . .