Even though almost all Java programmers either use JUnit or TestNG for their unit testing need along with some mock object generation libraries e.g. Mockito, but not everyone spends time and effort to learn subtle details of these testing libraries, at least not in proportion to any popular framework like Spring or Hibernate. In this blog post, I am sharing one of such detail, which has puzzled me a couple of years ago. At that time, though I had been using JUnit for a significant time, I wasn't aware that code written inside the constructor of the Test class is executed before each test method.