"Harden not your provocation, in the day of temptation in the wilderness: when your fathers tempted me, proved me, and saw my works for forty years," (cf. Heb. 3:9).
In Hebrew, the word for testing can be interpreted to imply that one is already guilty and they must consequently have the burden of proof of one's innocence: contrary to our right to be considered innocent till proven guilty. The Israelites lacked faith and tried God's patience and therefore were tested in the Wilderness before being ready to enter the Promised Land. What they conceived was nothing short of treason against God and Moses and to see if God was "worth following." They came to the conclusion this God-thing was working well for them and longed for the "good old days" in Egypt.
But they were not living in reality because they didn't have faith in God and know that He always acts in character and that's why and how we can know Him. It isn't all a matter of what works for you or what the end result is (pragmatic) but what is true that matters in the final analysis. Plato said something very pertinent: "If I want to know how to live in reality, I must know what God is really like" God can be our Exemplar and we can emulate Him because we can see Jesus. The Israelites failed to believe in the God who is and worshiped their own figment of their imagination., a concocted and ill-conceived image of God in their own box. We must accept God for who He is and not what we want Him to be for us. It doesn't matter how strongly one believes error, it's still false; truth doesn't depend on whether one believes it or not; we can have false convictions and be sincerely wrong.
God will make an impression on our hearts as we come to know Him in reality and we found out that He is true to Himself with no hypocrisy or contradiction. Gideon put God to the test with fleece and David said we should "taste and see that the LORD is good." In Malachi God challenges us to liberality in giving in exchange for blessing, to find out that we cannot out-give God. But Jesus was tested by Satan and he challenged Christ to jump off a cliff to see if God's Word would prove true. This is the kind of testing that is sin; assuming we can make God prove Himself on purpose to test Him when we should know better.
As Christians, we don't just believe in God, but in the God who is there! We don't just believe He exists, but that He is the God who does exist. We believe in the God who indwells us, that He is real and not silent. He's not dead but the God who won't die! This kind of faith doesn't come from nothing but the experience of walking with the LORD. Soli Deo Gloria!