improve some test

[javeme]

Change-Id: I4063e5690fe1ed0c1c5556302881a24518ac4424

[javeme]

not sure whether to enable

[codecov]

Codecov Report

Merging #139 (f152571) into master (ba79813) will increase coverage by 0.69%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #139      +/-   ##
============================================
+ Coverage     77.18%   77.88%   +0.69%     
- Complexity      947      962      +15     
============================================
  Files           154      154              
  Lines          4042     4042              
  Branches        241      241              
============================================
+ Hits           3120     3148      +28     
+ Misses          743      716      -27     
+ Partials        179      178       -1     

Impacted Files	Coverage Δ
...in/java/com/baidu/hugegraph/driver/HugeClient.java	84.48% <0.00%> (+5.17%)	⬆️
...java/com/baidu/hugegraph/api/graphs/GraphsAPI.java	47.36% <0.00%> (+5.26%)	⬆️
...java/com/baidu/hugegraph/driver/GraphsManager.java	30.76% <0.00%> (+7.69%)	⬆️
.../com/baidu/hugegraph/driver/HugeClientBuilder.java	84.74% <0.00%> (+37.28%)	⬆️

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