Test Shots to Reveal Sensor Cleanliness

The best surface to photograph for sensor cleanliness test shots that I have found is an expanse of clear blue sky; every little speck, spot, and blemish will stand out like a sore thumb.
However, clear blue skies are very rare around here.
I would like to hear some ideas for replicating the blue sky scene indoors.

I have taken shots of various common indoor surfaces, but they show up rough as a cob when photographed.

Stop the lens down and point it at a mostly plain colored wall. Make sure you're at ISO 100. Set the focus to far away and hold the camera close to the wall. You can probably eek out a 2-4 second exposure, and you can drag the camera along the direction of the wall, this would blur out anything if it WERE in focus and your sensor spots will most definitely show up.

Silver-Halide wrote in post #18991695
you can drag the camera along the direction of the wall

Thanks ! I am going to put that information in my keeper file.

Please explain this "drag the camera" bit; are you meaning I should ease up closer while the shutter is open, or use a side-to-side panning motion ?

I am anxious to experiment with this new knowledge. Thanks.

My method:
Light color, evenly lit, wall. Focus at infinity. ISO 100. Minimum aperture for lens (lens does not matter) in use. Keeping camera sensor parallel to wall, move camera in 8" to 12" circle during exposure. Speed of movement is mostly irrelevant. The point of movement is that ANYTHING that shows on your sensor, is ON YOUR SENSOR. There is some infinitesimal chance that internal lens dust will show up in these photos. If you suspect lens dust: change lens, repeat. If it shows up again, it wasn't in the lens.

Silver-Halide wrote in post #18991695
Stop the lens down and point it at a mostly plain colored wall. Make sure you're at ISO 100. Set the focus to far away and hold the camera close to the wall. You can probably eek out a 2-4 second exposure, and you can drag the camera along the direction of the wall, this would blur out anything if it WERE in focus and your sensor spots will most definitely show up.

PentaxShooter wrote in post #18991828
My method:
Light color, evenly lit, wall. Focus at infinity. ISO 100. Minimum aperture for lens (lens does not matter) in use. Keeping camera sensor parallel to wall, move camera in 8" to 12" circle during exposure. Speed of movement is mostly irrelevant. The point of movement is that ANYTHING that shows on your sensor, is ON YOUR SENSOR. There is some infinitesimal chance that internal lens dust will show up in these photos. If you suspect lens dust: change lens, repeat. If it shows up again, it wasn't in the lens.

Thanks !
I knew the sensor needed cleaning on account of several smudges in the blue sky shots; so, last night, I gave the sensor a thorough cleaning.
Inspecting it with my Carlson loupe showed it to be spotless.
Taking some test shots as per your instructions proved it to be clean as a whistle.

Good news! Enjoy your clean camera.