Unit Testing MapReduce Programs
• Unit Testing
• The JUnit and MRUnit Testing Framework• Writing Unit Tests with MRUnit
• Running Unit Tests
Delving Deeper into the Hadoop API
•  Using the ToolRunner Class
• Setting Up and Tearing Down Mappers 
and Reducers
• Decreasing the Amount of Intermediate
Data with Combiners
• Accessing HDFS Programmatically
• Using The Distributed Cache
• Using the Hadoop API’s Library of 
Mappers, Reducers, and Partitioners
Practical Development Tips  
and Techniques
• Strategies for Debugging MapReduce C
• Testing MapReduce Code Locally 
by Using LocalJobRunner
• Writing and Viewing Log Files
• Retrieving Job Information with Counter• Reusing Objects
• Creating Map-Only MapReduce Jobs
Partitioners and Reducers
• How Partitioners and Reducers  
Work Together
• Determining the Optimal Number  
of Reducers for a Job
• Writing Customer Partitioners
Data Input and Output
• Creating Custom Writable and
WritableComparable Implementations
• Saving Binary Data Using SequenceFile 
and Avro Data Files
• Issues to Consider When Using 
File Compression
• Implementing Custom InputFormats 
and OutputFormats