[improve][test] Add solution to PulsarMockBookKeeper for intercepting reads

[lhotari]

Motivation

In Pulsar tests, in-memory PulsarMockBookKeeper is used to implement BookKeeper client API.
There hasn't been a way to write realistic tests where there's variable latencies in BookKeeper reads.
Adding tests for various broker cache scenarios will benefit from this test framework improvement.

Example usage:

        // introduce delay to reads
        pulsarTestContext.getMockBookKeeper().setReadHandleInterceptor((ledgerId, firstEntry, lastEntry, entries) -> {
            log.info("intercepted read entries for ledgerId {}, firstEntry={}, lastEntry={}", ledgerId, firstEntry,
                    lastEntry);
            long delayMillis = ThreadLocalRandom.current().nextLong(25, 50);
            return CompletableFuture.supplyAsync(() -> entries,
                    CompletableFuture.delayedExecutor(delayMillis, TimeUnit.MILLISECONDS));
        });

The same approach can be used to inject failures.

Modifications

Add PulsarMockReadHandleInterceptor interface and implement it in PulsarMockBookKeeper.

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.16%. Comparing base (bbc6224) to head (c937b12).
Report is 861 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #23875      +/-   ##
============================================
+ Coverage     73.57%   74.16%   +0.58%     
+ Complexity    32624    31815     -809     
============================================
  Files          1877     1853      -24     
  Lines        139502   143619    +4117     
  Branches      15299    16311    +1012     
============================================
+ Hits         102638   106509    +3871     
+ Misses        28908    28727     -181     
- Partials       7956     8383     +427     

Flag	Coverage Δ
inttests	26.81% <ø> (+2.23%)	⬆️
systests	23.18% <ø> (-1.14%)	⬇️
unittests	73.66% <ø> (+0.81%)	⬆️

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