In order to get high-quality production code, it's not enough just to ensure maximum coverage with tests. No doubt, great results require the main project code and tests to work efficiently together. Therefore, tests have to be paid as much attention to as source code. A decent test is a key success factor, as it will catch regression in production. Let's take a look at PVS-Studio static analyzer warnings to see the importance of the fact that errors in tests are no worse than the ones in production. Today's focus: Apache Hadoop. 
About the Project
Those who were formerly interested in Big Data have probably heard or worked with the Apache Hadoop project. In a nutshell, Hadoop is a framework that can be used as a basis for building and working with Big Data systems.