Add a mock initiator implementation that allows tests to specify a list
of expected transactions.
Change-Id: Ifb5c1bedd9468202f11a380766e1ec4091055dae
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/92147
Reviewed-by: Mark Slevinsky <markslevinsky@google.com>
Commit-Queue: Austin Foxley <afoxley@google.com>
