Problem:
assert_log() only matches single lines. This was never an intentional
decision, it was merely a result of using read_file_list().
Note: any tests that indiscriminately match `.*` should be rewritten to
avoid (unlikely) "false positives". I checked all existing tests.
Solution:
Change assert_log() to match the concatenated lines instead of matching
per-line.
af4f7f1618