Assert an Exception is Thrown in

I have this Junit test in my project

public class CalculatorBookingTest {

    private CalculatorBooking calculatorBooking;

    @Rule
    public ExpectedException expectedException = ExpectedException.none();

    @Before
    public void setUp() {
        calculatorBooking = new CalculatorBooking();
    }

    @Test
    public void shouldThrowAnException_When_InputIsNull() {
        calculatorBooking.calculate(null, null, 0, null);
        expectedException.expect(CalculationEngineException.class);
        expectedException.expectMessage("Error");
    }

}

but when I run the test, the Exception is Thrown but nevertheless the test fail

You could do something like:

@Test(expected = CalculationEngineException.class)
public void shouldThrowAnException_When_InputIsNull() {
    calculatorBooking.calculate(null, null, 0, null);
}

From Junit doc :

> The Test annotation supports two optional parameters. The first,
> expected, declares that a test method should throw an exception. If it
> doesn't throw an exception or if it throws a different exception than
> the one declared, the test fails.

Place expectedException.expect before the call that will throw the exception.

@Test
public void shouldThrowAnException_When_InputIsNull() {
    expectedException.expect(CalculationEngineException.class);
    expectedException.expectMessage("Error");

    calculatorBooking.calculate(null, null, 0, null);

}

You need to first tell JUnit that the method is expected to throw the exception. Then when it's thrown - it knows that the test passes. In your code you put expect() after the exception is thrown - so the execution doesn't even go that far. The right way:

@Test
public void shouldThrowAnException_When_InputIsNull() {
    expectedException.expect(CalculationEngineException.class);
    expectedException.expectMessage("Error");

    calculatorBooking.calculate(null, null, 0, null);

}