Whilst a proper shutter tester is the best and most accurate way to measure a camera shutter (see my other shutter tester)
Sometimes optical confirmation can be useful, or if using a digital camera, traditional film camera testers cannot be used.
This device is a very simple moving LED bar, which can be set to strobe at standard camera shutter speeds 1/32, 1/64, 1/128, 1/256 & 1/1024s by pushing the button. (Note these are the genuine speeds, not the humanised 1/30, 1/125, 1/250...) speeds
Each row of LEDs is illumintaed to the set time (1/32s) for example, then extingished as the next row lights.
Setting the LEDs to strobe at the same as the camera shutter speed will result in two (sometimes one) line of LEDs being photograped (using a digital camera). If 3 or more rows are photographed, then it is an indication that the shutter speed is slow. (Set tke LEDs to 1/512 but the camera to 1/30, to see this effect)
For a film camera, remove the lens, open the back of the camera. When the shutter is operated you will see through the camera to the LED matrix. You will see the ame LED pattern as decribed above.
Only four parts are required, Arduino Nano (or Uno) board, LED matrix Push-button (This is not even needed, you could just touch two wires togeher) Two Dupont wires (or any bit of wire if you want to solder directly to the Arduino board)
Parts & links to them, as well as build docs * firmware are all in the files.