Proper way to apply and test a small kernel patch?

[John W <jwdevel@gmail.com>]

Hello,

I want to apply a small patch, then test the new kernel. If it fails,
I want to be able to return to my previous stable one.

Towards that end, I am following this guide:
https://kernel-team.pages.debian.net/kernel-handbook/ch-common-tasks.html#s4.2.2

That generally worked; the `test-patches` script incorporated my
patch, compiled the kernel, and produced .deb files in the directory
above.

However, when I try to install the .deb it fails (apologies for poor
line-wrapping, gmail is weak in this regard):

    $ sudo dpkg -i
linux-image-4.19.0-5-amd64-unsigned_4.19.37-5+deb10u2a~test_amd64.deb
    [sudo] password for jrw:
    Selecting previously unselected package linux-image-4.19.0-5-amd64-unsigned.
    dpkg: considering removing linux-image-4.19.0-5-amd64 in favour of
linux-image-4.19.0-5-amd64-unsigned ...
    dpkg: no, cannot proceed with removal of
linux-image-4.19.0-5-amd64 (--auto-deconfigure will help):
     linux-image-amd64 depends on linux-image-4.19.0-5-amd64
      linux-image-4.19.0-5-amd64 is to be removed.

    dpkg: regarding
linux-image-4.19.0-5-amd64-unsigned_4.19.37-5+deb10u2a~test_amd64.deb
containing linux-image-4.19.0-5-amd64-unsigned:
     linux-image-4.19.0-5-amd64-unsigned conflicts with
linux-image-4.19.0-5-amd64
      linux-image-4.19.0-5-amd64 (version 4.19.37-5+deb10u1) is
present and installed.

    dpkg: error processing archive
linux-image-4.19.0-5-amd64-unsigned_4.19.37-5+deb10u2a~test_amd64.deb
(--install):
     conflicting packages - not installing linux-image-4.19.0-5-amd64-unsigned
    Errors were encountered while processing:
     linux-image-4.19.0-5-amd64-unsigned_4.19.37-5+deb10u2a~test_amd64.deb


So, it seems that this "a~test" kernel is seen as conflicting with my
current installed kernel.

How do I overcome this?
I assume this is an everyday task, but I'm not familiar enough to know
what to  tweak.

Maybe I can make it use a fake version number (like "99.99") somewhere?

Thanks
-John