13.5. Expected Exceptions

Verifying expected exceptions

The following Calculator class has a divide method that should throw an exception if denominator is equal to zero.

public class Calculator {

  public static int sum(int value1, int value2) {
      return value1 + value2;
  }

  public static int multiply(int value1, int value2) {
      return value1 * value2;
  }

  public static int divide(int numerator, int denominator) {
      return numerator / denominator;
  }
}

We can verify that behavior via the assertThrows method, as shown below.

@Test
void divisionByZeroThrowsException() {
  assertThrows(ArithmeticException.class, () -> {
      Calculator.divide(1, 0);
  });
}

Note that:

• The first parameter of assertThrows is the exception type you expect to be thrown.
• The second parameter is the code you expect to throw the exception.

Exercise

Write test methods that verify if the get method of ArrayList throws an IndexOutOfBoundsException when passing an index out of range (index < 0 or index >= size()).

1. Test index -1 on an non-empty list.
2. Test index 0 on an empty list.
3. Test index 1 on a list with a single element.
4. Test index 5 on a list with 5 elements.
5. Test that getting the element on index 0 of a non-empty list does not throw an exception using the method assertDoesNotThrow.