It's probably not worth adding the C test files to regular formatting as
they're pretty much never touched, but ensuring the files are formatted
according to our standards and getting rid of warnings is a cheap
one-time fix.
In order to run unittests with a release build, we need the test
functions to be accessible when NDEBUG is defined. Moving the functions
into the test fixture ensures they are available and only available for
use by the unit tests.
