How do you verify that your program works correctly?

I use the following approaches:

• Unit testing: I test individual components or methods in isolation. For this, I use frameworks like JUnit or TestNG.

  // Example of a unit test with JUnit
  import org.junit.jupiter.api.Test;
  import static org.junit.jupiter.api.Assertions.*;
  
  class CalculatorTest {
  
      @Test
      void testAdd() {
          Calculator calculator = new Calculator();
          assertEquals(5, calculator.add(2, 3), "Sum should be 5");
      }
  }
  
  class Calculator {
      public int add(int a, int b) {
          return a + b;
      }
  }
  

• Integration testing: I check the interaction between different modules or system components. This may include testing database interactions, external services, etc.

• Functional testing: I verify whether the program meets the specified requirements. I focus on the system's behavior from the user's perspective.

• System testing: I test the entire system as a whole, including all subsystems and their interactions.

• Load testing: I evaluate the system's performance under high load to identify bottlenecks and determine the maximum number of users the system can handle. I use tools like JMeter or Gatling.

• Security testing: I check for system vulnerabilities and compliance with security requirements.

• Logging and monitoring: I embed detailed logging into the code and use monitoring systems (e.g., Prometheus, Grafana) to track the application's performance in real-time. This helps identify errors and performance issues in production.

• Code review: I review colleagues' code to identify potential issues before deployment.

• Test automation: I automate all types of testing as much as possible to ensure quick and reliable feedback when making changes to the code. For UI testing automation, I use Selenium.

• Exception handling: I use try-catch blocks and other exception handling mechanisms for graceful degradation when errors occur.

  // Example of exception handling
  try {
      // Code that may throw an exception
      int result = 10 / 0;
  } catch (ArithmeticException e) {
      // Handle the exception
      System.err.println("Error: Division by zero!" + e.getMessage());
      // You can also log the error
  }
  

The choice of specific methods depends on the project type, its complexity, and criticality.