Minor: add javadoc to test #425

Job	Run time
CheckerFramework (JDK 11)	10m 20s
Linux (JDK 11), Avatica main	11m 46s
Error Prone (JDK 11), latest Guava	4m 1s
CheckerFramework (JDK 11), oldest Guava	10m 11s
Druid Tests	6m 49s
Linux (JDK 11), Pacific/Chatham Timezone	10m 37s
Linux (JDK 21)	10m 6s
Linux (JDK 17)	10m 23s
Linux (JDK 22)	11m 53s
Linux (JDK 8), latest Guava, America/New_York Timezone	12m 11s
Linux (JDK 8) Slow Tests	0s
Linux (JDK 8), oldest Guava, America/New_York Timezone	10m 58s
macOS (JDK 21)	38m 51s
Windows (JDK 17)	14m 41s
Windows (JDK 21)	15m 18s
Windows (JDK 8)	15m 58s
	3h 14m 3s

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