Should modify filesCompacting under storeWriteLock

java.lang.IllegalArgumentException
	at org.apache.hbase.thirdparty.com.google.common.base.Preconditions.checkArgument(Preconditions.java:131)
	at org.apache.hadoop.hbase.regionserver.compactions.SortedCompactionPolicy.getCurrentEligibleFiles(SortedCompactionPolicy.java:173)
	at org.apache.hadoop.hbase.regionserver.compactions.SortedCompactionPolicy.preSelectCompactionForCoprocessor(SortedCompactionPolicy.java:44)
	at org.apache.hadoop.hbase.regionserver.DefaultStoreEngine$DefaultCompactionContext.preSelect(DefaultStoreEngine.java:130)
	at org.apache.hadoop.hbase.regionserver.HStore.requestCompaction(HStore.java:1438)
	at org.apache.hadoop.hbase.regionserver.HStore.requestCompaction(HStore.java:1419)
	at org.apache.hadoop.hbase.regionserver.HRegion.compact(HRegion.java:2238)
	at org.apache.hadoop.hbase.coprocessor.example.TestWriteHeavyIncrementObserver.test(TestWriteHeavyIncrementObserver.java:70)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:59)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:56)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.runners.ParentRunner$3.evaluate(ParentRunner.java:306)
	at org.junit.runners.BlockJUnit4ClassRunner$1.evaluate(BlockJUnit4ClassRunner.java:100)
	at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:366)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:103)
	at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:63)
	at org.junit.runners.ParentRunner$4.run(ParentRunner.java:331)
	at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:79)
	at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:329)
	at org.junit.runners.ParentRunner.access$100(ParentRunner.java:66)
	at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:293)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
	at org.apache.hadoop.hbase.SystemExitRule$1.evaluate(SystemExitRule.java:38)
	at org.junit.internal.runners.statements.FailOnTimeout$CallableStatement.call(FailOnTimeout.java:299)
	at org.junit.internal.runners.statements.FailOnTimeout$CallableStatement.call(FailOnTimeout.java:293)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.lang.Thread.run(Thread.java:748)