Create unit tests for darkness-checking logic

[domdomegg]

Summary:

Would be good to have a unit test for the darkness checking algorithm. It could use the 4 images in #1767 as samples.

See #2639 (comment)

[domdomegg]

For someone picking this up: it might be useful to reuse the generate image methods from #2626

[misaochan]

Added beginner-friendly label, this would be great for a GSoC/Outreachy student.

[silkypriya]

Hello @domdomegg @misaochan can i work on this issue ?

[maskaravivek]

Sure take this up @silkypriya

[misaochan]

Go for it! :)

[silkypriya]

Created PR #2727 for this.
Kindly review. Thank you!

[ciphereck]

@misaochan @maskaravivek @nicolas-raoul
Can I work on closing this issue?

[maskaravivek]

Yes, sure. It is yours.

[ciphereck]

I wrote some tests of ImageUtils class. But I'm not able to run it. It shows error "No tests were found".
I try to run tests using both ImageUtilsTest Class and the test function I created. But it's showing the same error. It's showing the same error, for tests written in the past as well by someone else.
Also, some test classes are giving NoClassDefFoundError while testing.
Can anyone help? @maskaravivek @nicolas-raoul