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### _Why are the changes needed?_
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Improve test coverage.
### _How was this patch tested?_
Pass `org.apache.kyuubi.engine.spark.SchedulerPoolSuite`.
Closes#543 from ulysses-you/add-scheduler-pool-test.
Closes#543
f5563b1 [ulysses-you] trait
57938a1 [ulysses-you] init
Authored-by: ulysses-you <ulyssesyou18@gmail.com>
Signed-off-by: ulysses-you <ulyssesyou18@gmail.com>
cacc2b05b3