Arrange/Act/Assert (AAA) is a pattern for organizing unit tests.

This structure makes the code easier to read and understand. You should format your code to separate these steps.

1. Arrange: setup and initialization required for the test
2. Act: call methods to test
3. Assert: Verify the outcomes

For example we have a class that sums up two numbers:

  
public class SumUp {
    public int add (int firstNumber, int secondNumber) {
        return firstNumber+secondNumber;
    }
}
  

And we have a class with tests that are created according to AAA. Creation of the object and initialization of int - is an Arrange part. Calling the method sumUp.add() is an Act part. And assert is an Assert part.

  
    public class SumUpTests {
    
    @Test
    public void testSum() {
        SumUp sumUp = new SumUp();
        int firstNumber = 5;
        int secondNumber = 2;

        int result = sumUp.add(firstNumber, secondNumber);

        Assert.assertEquals(result, 7);
    }
    
}
  

Summary:

1 – Easier to read, maintain, and enhance

2 – Useful for unit tests