Why has god forbidden us to 'put him to the test'?

Because leaders don't like to be questioned. Just ask Mao Zedong, Hitler, Stalin, etc...

You need to read the rest of the bible and not just pick one verse out of context.

In that section, Moses taught the Israelites all that God had ordered him to teach.

It basically meant: You must remember the commandments that I am giving to you today.

It's similar to like how little children complain about their parents rules and rebel against them, even though those rules are set for their own safety and well being, etc. Basically saying understand your parent knows what is best for you even if at the time you might consider it a restriction.

‘If you love me, you will obey my commandments.’ (See John 14:15)

Christians today can easily do the same thing, attempting to bend or ignore rules when it suits them. They may go to church one day of the week on Sunday. They may even read the Bible and pray. But those things have no value unless Christians behave in the right way too. Then that will show that they love God.

It's not good enough to just go: maybe this is just a little white lie, maybe I can bend that rule to allow this and that, etc. As little kids test their parent's rules and try make excuses to get around them, so do people test God's rules to avoid following them.

As for actually questioning God...

In Judges 6:13-14 (NIV) we read:

"But sir," Gideon replied, "if the Lord is with us, why has all this happened to us? Where are all his wonders that our fathers told us about when they said, 'Did not the Lord bring us up out of Egypt?' But now the Lord has abandoned us and put us into the hand of Midian."

Gideon just questioned God's goodness, His power, and His promises. That is pretty heavy. The amazing thing is that the Lord did not chastise Gideon's questioning spirit. Rather, He answers Gideon with a task to accomplish to prove/show it.

How people can still believe in the textuality of a 2000 year old book in 2013 boggles the mind..........

Because apparently the all knowing God is well not all knowing.

he is saving you from being the loser , now that's what I call charitable and loving.

That's how bullshit thrives - by forbidding tests.

Just be quiet and don't forgot to pay your dues.