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Examples: SleepDistributedTest.java, MultiThreadedIntegrationTest

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• Expected vs unexpected exceptions in tests
• Never catch unexpected exceptions. That is bad... way bad...
• Special case: Asynchronous actions may need to catch checked exceptions and use ErrorCollector
• Use method throws clause for unexpected exceptions 
• The alternative serves to make failures more opaque. 
• Fixing test failures (as you will have to do at some point) is all about visibility into the problems of the test. 
• Use AssertJ catchThrowable or assertThatThrown for expected exceptions
• Avoid using JUnit expected exception support such as ExpectedException Rule or Test annotation expected element. Example: @Test(expected = Exception.class) 
• Remember to catch specific exceptions, not whole parent classes. If someone adds an additional exception, will it break your test?

Examples: ErrorHandlingTest, ExpectedExceptionTest

Sometimes you think they’re helping...

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• Use ExecutorServiceRule or DistributedExcutorServiceRule
• Provides debugging support for hangs
• Cleans up threads on tear down
• Test task code should be interruptible
• Use Future or CompletableFuture for submitted runnable/callable
• Always invoke get() on any Future or CompletableFuture

Examples: AsyncErrorHandlingTest, ExecutorSyncHangIntegrationTest, ExecutorLockHangIntegrationTest, ExecutorErrorHandlingDistributedTest

Handling exceptions in callbacks

• Avoid catching exception and setting some test state to check later
• Use ErrorCollector in unit and integration tests
• Use SharedErrorCollector in distributed tests

Examples: AsyncErrorHandlingIntegrationTest, AsyncErrorHandlingDistributedTest

AsyncInvocation usage

• Timeout now gets a remote stack trace to use as the cause and dumps stack traces for that JVM’s threads
• Always use await() or get()
• Both check and throw any remote exceptions
• Both use GeodeAwaitility Timeout and will throw TimeoutException if it’s exceeded
• Use await() for Void types and get() when expecting a non-null value

Examples: AsyncInvocationDistributedTest, AsyncInvocationHangDistributedTest

Know your DUnit Rules

• DistributedRule -- simply launches DUnit and greps for suspect strings after each test method
• DistributedExecutorServiceRule -- provides an ExecutorService for all VMs
• DistributedRestoreSystemProperties -- restores system properties in all VMs
• SharedCountersRule -- shares counters across all VMs
• SharedErrorCollector -- shares one JUnit ErrorCollector across all VMs

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