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Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
Testing Hadoop jobs with MRUnit
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Testing Hadoop jobs with MRUnit

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Real-world examples and struggles with MRUnit testing Hadoop MapReduce jobs.

Real-world examples and struggles with MRUnit testing Hadoop MapReduce jobs.

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    • 1. Testing Hadoop jobs with MRUnit © 2010 Eric Wendelin
    • 2. Eric Wendelin Hadooper at Return Path Blog: eriwen.com Twitter: @eriwen
    • 3. What is MRUnit? • Testing library for MapReduce • Developed by Cloudera • Easy integration between MapReduce and standard testing tools (e.g. JUnit)
    • 4. Why do I need that?
    • 5. Testing without MRUnit • Write tests that create JobConf or Configuration objects • conf.set(‘mapred.job.tracker’, ‘local’) • Developing new test input files stored alongside MapReduce test code • Lots of work to validate output files • External file I/O makes tests slooooow
    • 6. MRUnit makes testing Hadoop jobs easier
    • 7. Testing with MRUnit • No external test input or output files • Programmatically specified • Less test harness code (but also perhaps less control) • Concise, fast tests
    • 8. class ExampleTest() { private Example.MyMapper mapper private Example.MyReducer reducer private MapReduceDriver driver @Before void setUp() { mapper = new Example.MyMapper() reducer = new Example.MyReducer() driver = new MapReduceDriver(mapper, reducer) } @Test void testMapReduce() { driver.withInput(new Text(‘a’), new Text(‘b’)) driver.withOutput(new Text(‘c’), new Text(‘d’)) driver.runTest() } }
    • 9. class ExampleTest() { private Example.MyMapper mapper private Example.MyReducer reducer private MapReduceDriver driver @Before void setUp() { mapper = new Example.MyMapper() reducer = new Example.MyReducer() driver = new MapReduceDriver(mapper, reducer) } @Test void testMapReduce() { driver.withInput(new Text(‘a’), new Text(‘b’)) .withOutput(new Text(‘c’), new Text(‘d’)) .runTest() } }
    • 10. Test map and reduce separately
    • 11. class ExampleTest() { private Example.MyMapper mapper private MapDriver mDriver @Before void setUp() { mapper = new Example.MyMapper() driver = new MapDriver(mapper) } @Test void testMap() { mDriver.withInput(new Text(‘a’), new Text(‘b’)) mDriver.withOutput(new Text(‘c’), new Text(‘d’)) mDriver.runTest() } }
    • 12. class ExampleTest() { private Example.MyReducer reducer private ReduceDriver rDriver @Before void setUp() { rDriver = new Example.MyReducer() driver = new ReduceDriver(reducer) } @Test void testReduce() { rDriver.withInput(new Text(‘a’), [new Text(‘foo’), new Text(‘bar’)]) rDriver.withOutput(new Text(‘c’), new Text(‘d’)) rDriver.runTest() } }
    • 13. Counters!
    • 14. driver.withInput(...) driver.run() def counters = driver.getCounters() assertEquals(1, counters.findCounter (‘foo’, ‘bar’).getValue())
    • 15. Verifying logging
    • 16. def messages = [] def appender = [ append: { messages.add(it) }, requiresLayout: { false } ] as AppenderSkeleton Logger.getRootLogger().addAppender(appender) driver.runTest() assertTrue messages.find { it.getLevel.toString() == ‘WARN’ && it.getMessage().contains(‘My err’) } Logger.getRootLogger().removeAppender(appender)
    • 17. Cool stuff I haven’t tried... • The PipelineMapReduceDriver - allows testing a series of MapReduce passes • Just call addMapReduce(mapper, reducer) • Mock objects - MockReporter, MockInputSplit, and MockOutputCollector • Test combiners with myMapReduceDriver.setCombiner(myCombiner)
    • 18. Problems with MRUnit
    • 19. runTest() does not give meaningful information on failure
    • 20. Better to use run() and then assert
    • 21. driver.setInput(new Text(‘foo’), new Text(‘bar’)) def output = driver.run() assertEquals ‘baz’, output[0].first assertEquals ‘jy’, output[0].second
    • 22. Documentation is severely lacking
    • 23. runXxx() calls setup() called for new Hadoop API, but not old API
    • 24. Tests are not executed in a distributed way
    • 25. In Summary, MRUnit... • Makes testing your Hadoop jobs easier • Abstracts away a lot of the boilerplate test setup you need • Has it’s problems • but they are outweighed by the benefits
    • 26. cloudera.com/hadoop-mrunit Blog: eriwen.com Twitter: @eriwen Email: eric.wendelin@returnpath.net © 2010 Eric Wendelin

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