Republished articles with source attribution. This collection is separate from Diary Coding’s original guides and does not display ads.
Short answer Unit test behavior that you own and that can break, especially logic with branches, rules, edge cases, and important failure paths. Do not unit test code that merely repeats the framework, language, or library behavior unless you add meaningful logic around it. Good candidates for unit tests 1. Business rules If the code […]
Writing JUnit tests is not only about checking whether the code works. Good tests should be clear, reliable, independent, and easy to maintain. Here are common mistakes beginners often make when writing JUnit tests, along with better ways to avoid them. 1. Do Not Let Tests Depend on Each Other Each test should be able […]
The Arrange-Act-Assert pattern is a simple way to organize unit tests so they are easy to read and understand. A unit test usually answers three questions: Arrange: What data or objects do I need? Act: What behavior am I testing? Assert: What result do I expect? Basic Structure @Test void methodName_expectedBehavior() { // Arrange // […]
Clean JUnit tests should be easy to understand, focused on one behavior, and safe to change. A good test should tell you: What scenario is being tested What action happens What result is expected Most Java projects today should use JUnit 5, from the org.junit.jupiter package. 1. Use Clear Test Names A test name should […]
Organizing Tests with Nested Test Classes Nested test classes are a great way to group related tests inside a single test class. In Java, this is commonly done with JUnit 5 using @Nested. They help you structure tests around: A specific method A scenario A state of the object under test Success vs failure cases […]
In JUnit 5, you can add readable names to your tests using the @DisplayName annotation. @DisplayName lets you show a friendly, human-readable test name in test reports and IDE test runners instead of relying only on the Java method name. Example import org.junit.jupiter.api.DisplayName; import org.junit.jupiter.api.Test; import static org.junit.jupiter.api.Assertions.assertEquals; class CalculatorTest { @Test @DisplayName("Adding two positive […]
Stay curious. There is always something new to learn.
Writer and founder of Diary Coding — sharing notes, tutorials, and experiences about programming for anyone who wants to keep learning.