Spring Boot provides a robust environment for testing applications with its seamless integration with JUnit. However, as you dive deeper into testing your applications, you might encounter the notorious IllegalStateException. This exception often leaves developers puzzled because it signals an issue with the application context or test configuration. Understanding the root causes and systematically addressing them is key to successful debugging. In this article, we’ll explore the reasons behind this exception, analyze related scenarios, and provide detailed code examples to guide you through resolving these issues.