Testing Hadoop jobs with MRUnit

23,282 views
23,115 views

Published on

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

Published in: Technology

Testing Hadoop jobs with MRUnit

  1. 1. Testing Hadoop jobs with MRUnit © 2010 Eric Wendelin
  2. 2. Eric Wendelin Hadooper at Return Path Blog: eriwen.com Twitter: @eriwen
  3. 3. What is MRUnit? • Testing library for MapReduce • Developed by Cloudera • Easy integration between MapReduce and standard testing tools (e.g. JUnit)
  4. 4. Why do I need that?
  5. 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. 6. MRUnit makes testing Hadoop jobs easier
  7. 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. 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. 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. 10. Test map and reduce separately
  11. 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. 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. 13. Counters!
  14. 14. driver.withInput(...) driver.run() def counters = driver.getCounters() assertEquals(1, counters.findCounter (‘foo’, ‘bar’).getValue())
  15. 15. Verifying logging
  16. 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. 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. 18. Problems with MRUnit
  19. 19. runTest() does not give meaningful information on failure
  20. 20. Better to use run() and then assert
  21. 21. driver.setInput(new Text(‘foo’), new Text(‘bar’)) def output = driver.run() assertEquals ‘baz’, output[0].first assertEquals ‘jy’, output[0].second
  22. 22. Documentation is severely lacking
  23. 23. runXxx() calls setup() called for new Hadoop API, but not old API
  24. 24. Tests are not executed in a distributed way
  25. 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. 26. cloudera.com/hadoop-mrunit Blog: eriwen.com Twitter: @eriwen Email: eric.wendelin@returnpath.net © 2010 Eric Wendelin

×