Add unit tests to fuzzers

[asraa]

Description
Add unit test styles to test expectations for simple fuzz test cases and utility functions used by the fuzzer.

Background
CVE-2019-15225 (#8519) was caused by recursive algorithms for matching regular expressions, especially those with '*' or '+' quantifiers. These are simple regular expressions that, when matched with very long URI, should have been caught by a timeout in our route resolution fuzzer.

However, route_fuzz_test was unable to catch this error due to a logical error in a utility function that resulted in headers created by the fuzz engine to not be ignored by default (#8653).
Moreover, fuzzers didn't explore any interesting configurations for HeaderMatchers, which specify the set of headers the route should match on. Between ignoring :path headers by default, and without a full enough corpus to cover different behaviors of route matching, the fuzzer never caught this CVE.

Proposal

• Functions used inside in the fuzzer, especially utility functions that parse inputs to the fuzzer should have unit style tests to confirm their expected behavior.
• In addition, we should add corpus entries for any configurations consumed by the fuzz target that appear in existing unit tests and integration tests.
• Any PRs that add regression tests or security critical tests should also include corpus entries for fuzzers.

[stale]

This issue has been automatically marked as stale because it has not had activity in the last 30 days. It will be closed in the next 7 days unless it is tagged "help wanted" or other activity occurs. Thank you for your contributions.

[stale]

This issue has been automatically closed because it has not had activity in the last 37 days. If this issue is still valid, please ping a maintainer and ask them to label it as "help wanted". Thank you for your contributions.