Re:Reply from actual kernel developer please . . . (Score 1)

I'm a developer and was wondering what kind of testing is done to verify the code.

Short answer: all kinds of testing.

• Ingo Molnar (among others) have access to huge build farms that compile- and boot-test the kernel.
• linux-next merges and builds proposed trees, and generates daily reports.
• Thousands of developers test development kernels before the stable kernel is released, each focusing on their area of interest.
• The kernel oops project tracks which kernel bugs occur most frequently.

Do they use unit testing? Regression testing?

Yes. See the Linux Test Project.