This is especially useful for large repositories (e.g. monorepos) that
use a hierarchical file system organization for nested test paths.
src/*/tests
The implementation uses the standard `glob` module to perform wildcard
expansion in Config.parse().
The related logic that determines whether or not to include 'testpaths'
in the terminal header was previously relying on a weak heuristic: if
Config.args matched 'testpaths', then its value was printed. That
generally worked, but it could also print when the user explicitly used
the same arguments on the command-line as listed in 'testpaths'. Not a
big deal, but it shows that the check was logically incorrect.
Now that 'testpaths' can contain wildcards, it's no longer possible to
perform this simple comparison, so this change also introduces a public
Config.ArgSource enum and Config.args_source attribute that explicitly
names the "source" of the arguments: the command line, the invocation
directory, or the 'testdata' configuration value.
Jon Parise