Add unit test for CountTelnetHandler

[icankeep]

What is the purpose of the change

see more from #7842

Brief changelog

Add unit test for CountTelnetHandler

• Make sure there is a GitHub_issue field for the change (usually before you start working on it). Trivial changes like typos do not require a GitHub issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue.
• Format the pull request title like [Dubbo-XXX] Fix UnknownException when host config not exist #XXX. Each commit in the pull request should have a meaningful subject line and body.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit-test to verify your logic correction, more mock a little better when cross module dependency exist. If the new feature or significant change is committed, please remember to add sample in dubbo samples project.
• Run mvn clean install -DskipTests=false & mvn clean test-compile failsafe:integration-test to make sure unit-test and integration-test pass.
• If this contribution is large, please follow the Software Donation Guide.

[codecov-commenter]

Codecov Report

Merging #7846 (1fddcb9) into master (0049c24) will increase coverage by 0.08%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #7846      +/-   ##
============================================
+ Coverage     59.49%   59.57%   +0.08%     
+ Complexity      557      556       -1     
============================================
  Files          1086     1086              
  Lines         43844    43844              
  Branches       6399     6399              
============================================
+ Hits          26084    26121      +37     
+ Misses        14875    14826      -49     
- Partials       2885     2897      +12     

Impacted Files	Coverage Δ	Complexity Δ
...che/dubbo/remoting/transport/mina/MinaChannel.java	35.52% <0.00%> (-10.53%)	14.00% <0.00%> (-1.00%)
.../apache/dubbo/rpc/protocol/AsyncToSyncInvoker.java	62.06% <0.00%> (-10.35%)	0.00% <0.00%> (ø%)
...ng/transport/dispatcher/all/AllChannelHandler.java	82.75% <0.00%> (-6.90%)	0.00% <0.00%> (ø%)
...dubbo/remoting/exchange/support/DefaultFuture.java	80.34% <0.00%> (-6.84%)	0.00% <0.00%> (ø%)
...ting/exchange/support/header/HeartbeatHandler.java	90.69% <0.00%> (-2.33%)	0.00% <0.00%> (ø%)
...a/org/apache/dubbo/monitor/dubbo/DubboMonitor.java	86.66% <0.00%> (-1.91%)	16.00% <0.00%> (ø%)
.../src/main/java/org/apache/dubbo/rpc/RpcStatus.java	73.80% <0.00%> (+1.19%)	0.00% <0.00%> (ø%)
.../dubbo/remoting/transport/netty4/NettyChannel.java	64.35% <0.00%> (+2.97%)	0.00% <0.00%> (ø%)
...che/dubbo/remoting/telnet/support/TelnetUtils.java	98.88% <0.00%> (+3.33%)	0.00% <0.00%> (ø%)
...in/java/org/apache/dubbo/common/utils/JVMUtil.java	92.45% <0.00%> (+11.32%)	0.00% <0.00%> (ø%)
... and 1 more

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[xiaoheng1]

LGTM