[improve][test] Add test brokerReachThreshold for ThresholdShedderTest

[Technoboy-]

Motivation

More details are here #18598, so add this test to avoid regression.

Documentation

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

[codecov-commenter]

Codecov Report

Merging #18664 (b50f4eb) into master (cee697b) will increase coverage by 0.32%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master   #18664      +/-   ##
============================================
+ Coverage     47.06%   47.39%   +0.32%     
- Complexity     8956    10491    +1535     
============================================
  Files           592      698     +106     
  Lines         56313    68062   +11749     
  Branches       5844     7276    +1432     
============================================
+ Hits          26503    32255    +5752     
- Misses        26946    32208    +5262     
- Partials       2864     3599     +735     

Flag	Coverage Δ
unittests	47.39% <ø> (+0.32%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...er/metadata/v2/TransactionBufferSnapshotIndex.java	0.00% <0.00%> (-77.78%)	⬇️
.../metadata/v2/TransactionBufferSnapshotSegment.java	0.00% <0.00%> (-75.00%)	⬇️
...he/pulsar/broker/service/PrecisPublishLimiter.java	0.00% <0.00%> (-73.98%)	⬇️
.../metadata/v2/TransactionBufferSnapshotIndexes.java	0.00% <0.00%> (-71.43%)	⬇️
...roker/service/schema/SchemaCompatibilityCheck.java	6.25% <0.00%> (-56.25%)	⬇️
...rvice/schema/ProtobufSchemaCompatibilityCheck.java	0.00% <0.00%> (-50.00%)	⬇️
...n/java/org/apache/pulsar/PulsarVersionStarter.java	0.00% <0.00%> (-42.31%)	⬇️
...oker/transaction/buffer/metadata/v2/TxnIDData.java	0.00% <0.00%> (-20.00%)	⬇️
...r/service/schema/JsonSchemaCompatibilityCheck.java	5.40% <0.00%> (-16.22%)	⬇️
...ransaction/buffer/impl/TopicTransactionBuffer.java	58.13% <0.00%> (-15.99%)	⬇️
... and 171 more