test-lib-functions: assert correct parameter count

test-lib-functions: assert correct parameter count

Add assertions of the correct parameter count of various functions, in
particularly the wrappers for the shell "test" built-in.

In an earlier commit we fixed a bug with an incorrect number of
arguments being passed to "test_path_is_{file,missing}". Let's also
guard other similar functions from the same sort of misuse.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>