Go to Scriptures, if you would please.
James 1:13 says that God will never tempt any man with evil, nor can God Himself be tempted to do evil.
God gave us laws, and one of those laws was "Thou shalt not kill".
Therefore, he will not tell you to break one of his Ten Commandments. The Ten Commandments were a part of Mosaic Law (which we are not under as Christians), however the Ten Commandments give a basic outline of what God considers to be sin and most (except for the Sabbath Law) are still considered sin to this day.
God will not tell you to commit a sin, nor will He tempt you to do evil.
There is never a point in your life where God will tell you to, or want you to, commit any evil act.
Now, there's a good question about war and fighting in a war, and the Murder law seems to conflict with obeying man's governments as they are God-ordained, and the only answer I can give to that, is that killing in a war does not constitute "murder" unless you killed a defenseless target that you knew was defenseless beforehand.