How are cameras that have a fixed exposure/gain calibrated/tested on earth for space lighting?

I'll further explain with a hypothetical example of what I mean: ISRO launches a Mars-bound planetary science explorer, and a video camera on board is used to verify deployment of a magnetometer as it leaves Earth. The video camera has a fixed exposure and/or gain, so it has to be calibrated on Earth to ensure that the image from the camera will not be over/underexposed (thus occluding the deployment status of the high-gain antenna.)

Since there is a variety of objects in which the camera could be pointing at (Earth, space, or - worst case - the Sun) how are fixed exposure/gain cameras set up/tested to ensure that whatever they want to have in view is clearly visible?

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    $\begingroup$ They may use a test chamber with a well defined and controlled light source. There are sun simulators for spacecraft testing too. $\endgroup$ – Uwe Feb 5 at 9:10
  • $\begingroup$ @Uwe Aren't sun simulators mainly used for thermal testing? Additionally, how could a light source like the sun be approximated given how much brighter it is in space than anything else? $\endgroup$ – jos Feb 5 at 9:15
  • $\begingroup$ @jos go on, ask that as a new question. $\endgroup$ – Hobbes Feb 5 at 9:36
  • $\begingroup$ @Hobbes I'm not sure what Uwe said was the correct answer, though. $\endgroup$ – jos Feb 5 at 9:40
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    $\begingroup$ Uwe wasn't implying a sun simulator is used for camera calibration. He just gave an example of a test chamber with a well-defined light level. Camera calibration would use much lower light levels. $\endgroup$ – Hobbes Feb 5 at 10:05

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