add unit test to dubbo-registry/dubbo-registry-api and dubbo-registry/dubbo-registry-default

[lixiaojiee]

What is the purpose of the change

add unit test to dubbo-registry/dubbo-registry-api and dubbo-registry/dubbo-registry-default
#1690

Brief changelog

dubbo-registry/dubbo-registry-default/src/test/java/org/apache/dubbo/registry/dubbo/DubboRegistryTest.java

Verifying this change

ut pass

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• 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 integration-test in test module.
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[lovepoem]

Please merge origin/master to make ci success

[codecov-io]

Codecov Report

Merging #3053 into master will increase coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #3053      +/-   ##
============================================
+ Coverage     63.43%   63.46%   +0.03%     
  Complexity       75       75              
============================================
  Files           653      653              
  Lines         28261    28261              
  Branches       4820     4820              
============================================
+ Hits          17926    17937      +11     
+ Misses         8057     8053       -4     
+ Partials       2278     2271       -7

Impacted Files	Coverage Δ	Complexity Δ
.../remoting/transport/netty4/NettyClientHandler.java	75% <0%> (-11.12%)	0% <0%> (ø)
.../apache/dubbo/remoting/transport/AbstractPeer.java	58.69% <0%> (-2.18%)	0% <0%> (ø)
...he/dubbo/registry/multicast/MulticastRegistry.java	63.79% <0%> (-1.73%)	0% <0%> (ø)
...dubbo/metadata/support/AbstractMetadataReport.java	69.35% <0%> (-1.62%)	0% <0%> (ø)
...dubbo/remoting/exchange/support/DefaultFuture.java	71.81% <0%> (-1.35%)	0% <0%> (ø)
...pache/dubbo/remoting/transport/AbstractServer.java	47.91% <0%> (-1.05%)	0% <0%> (ø)
.../java/org/apache/dubbo/config/ReferenceConfig.java	57.57% <0%> (-0.76%)	0% <0%> (ø)
...pache/dubbo/registry/support/AbstractRegistry.java	81.2% <0%> (-0.76%)	0% <0%> (ø)
...mon/src/main/java/org/apache/dubbo/common/URL.java	45.9% <0%> (+0.14%)	0% <0%> (ø)	⬇️
...bo/remoting/transport/netty/NettyCodecAdapter.java	54.68% <0%> (+1.56%)	0% <0%> (ø)	⬇️
... and 8 more

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[lixiaojiee]

Please merge origin/master to make ci success

It has been processed.

[lovepoem]

LGTM