How do you test that a frame i the cramps is square?

To test if a frame is square, you can use the "3-4-5 triangle method." Measure 3 feet along one side of the frame, then measure 4 feet along the adjacent side and check the diagonal between these two points; it should measure exactly 5 feet if the frame is square. Alternatively, use a carpenter's square, placing it in the corners to ensure the angles are 90 degrees. Adjust as necessary until all corners are square.