What you’ll learn

How automated unit tests are developed, including the primary libraries for that. Why automated testing is important to the maintainability of a project and how it can be used in automated builds.

Also because the JUnit framework relies heavily on annotations we will look at what they are and how they are used.

Why start here?

Any software project of a reasonable size quickly gets past the point where manual testing of the functionality with each change is practical. Automated testing gives us reassurance that a project can be enhanced or refactored whilst avoiding regressions.

Adding well constructed tests for a method, showing the expected results from specific inputs can help clarify the intent of a method and also lead to confirmation that the method parameters are sensible (e.g. in name, type and order) for its goal.

Self Study

Reading Materials

• Annotations - geeks for geeks annotations in java, dev.java
  • Don’t worry about how to create annotations
• The official JUnit 5 user guide, which describes how to write tests, how test lifecycle works, what annotations are available, etc. JUnit 5 user guide
  • Important Sections: 1.4, 2.1-2.7, 4.1, 4.2
• Articles summarising JUnit 5 basics: @Test, assertions, lifecycle, visibility rules; Junit 5 basics, baeldung junit-5, vogella JUnit
• Maven surefire plugin (reference for how tests are run during a build) documentation
• Simple project example example

Video Materials

• Beginner-friendly tutorials on creating and running your first JUnit 5 tests
  • Creating and running a test (IntelliJ)
  • JUnit 5 Crash Course (first ~25mins)
• More advanced use of JUnit (up to ~30mins when it starts on Mockito) - Mastering Java Testing

Exercises

package com.example;

public class Calculator {
  public int add(int a, int b) {
    return a + b;
  }

  public int subtract(int a, int b) {
    return a - b;
  }

  public int multiply(int a, int b) {
    return a\ * b;
  }

  public int divide(int a, int b) {
    if (b == 0) {
      throw new IllegalArgumentException("Division by zero");
    }
    return a / b;
  }
}

package com.example;

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.\*;

class CalculatorTest {

  @BeforeEach
  void setUp() {}

  @Test
  void testAdd() {}

  @Test
  void testDivide() {}

  @Test
  void testDivideByZeroThrows() {}
}

public class StringUtilities {
    public boolean isPalindrome(String s) { ... }
    public List<String> splitCommaSeparatedLine(String s) { ... }
}

public class ExampleTest {
  @BeforeEach
  public void setup() {
    System.out.println("setting up test data");
    ...
  }

  @Test
  public void testExample1() {
    System.out.println("running test case 1");
    ...
  }
  @AfterAll
  public void closeConnections() {
    System.out.println("closing connections");
    ...
  }

  @BeforeAll
  public void createConnections() {
    System.out.println("creating connections");
    ...
  }
}

Reflection on key concepts in automated testing

• Explain why tests should be independent of each other. What benefit does this bring?
• Explain the difference between a test-case, a test class and a test suite. Why might we use test suites?
• Explain the Junit test lifecycle
• particularly how we can use this to re-use state or reset state between tests and why this is useful from a maintainability and performance perspective.
• Are there situations where a test case might not have any assertions?
• What might a test without assertions miss and how could it be improved?

What you’ll learn

How to write useful javadoc, how it is structured and why it is important.

Why start here?

Most classes and methods are used by people other than the original developer. Providing a concise description of what a class / method is for and how to use it ensures that the correct expectations are set and that the developer is not surprised by any results/behaviours.

Self Study

Reading Materials

• Wikipedia - Javadoc
• Oracle tool and specification - overview javadoc spec
• example style guide - javadoc-tool
• Examples;
• Java Util
• Apache Commons Lang

Video Materials

• Javadoc explainer
• Javadoc in IntelliJ

Key Concepts

• Good javadoc is more than comments on the implementation
• Javadoc should depend on context;
• frameworks should illustrate how code is written to run using them
• libraries should illustrate how they are to be used
• Links can be to other parts of the code or to external materials e.g. for more complete explanations.
• Javadoc on tests is as important as on the source;
• useful javadoc will help provide context around edge cases and unusual assertions of behaviour

Exercises

In these exercises focus on;

• usage of the core syntax elements; @param, @return, @throws, @see, @link
• what a user of the service needs to know
• example usage, particularly any edge cases
• what tests are showing you about specific methods and their behaviours, in particular any edge cases that may need more explanation.