How do you assert that a certain exception is thrown in JUnit tests?

 @Test(expectedException=IndexOutOfBoundsException.class) public void testFooThrowsIndexOutOfBoundsException() throws Exception { doThrow(IndexOutOfBoundsException.class).when(foo).doStuff(); try { foo.doStuff(); } catch (IndexOutOfBoundsException e) { assertEquals(IndexOutOfBoundsException .class, ex.getCause().getClass()); throw e; } } 

Here is another way to check method thrown correct exception or not.

My solution using Java 8 lambdas:

public static <T extends Throwable> T assertThrows(Class<T> expected, ThrowingRunnable action) throws Throwable { try { action.run(); Assert.fail("Did not throw expected " + expected.getSimpleName()); return null; // never actually } catch (Throwable actual) { if (!expected.isAssignableFrom(actual.getClass())) { // runtime '!(actual instanceof expected)' System.err.println("Threw " + actual.getClass().getSimpleName() + ", which is not a subtype of expected " + expected.getSimpleName()); throw actual; // throw the unexpected Throwable for maximum transparency } else { return (T) actual; // return the expected Throwable for further examination } } } 

You have to define a FunctionalInterface, because Runnable doesn't declare the required throws.

@FunctionalInterface public interface ThrowingRunnable { void run() throws Throwable; } 

The method can be used as follows:

class CustomException extends Exception { public final String message; public CustomException(final String message) { this.message = message;} } CustomException e = assertThrows(CustomException.class, () -> { throw new CustomException("Lorem Ipsum"); }); assertEquals("Lorem Ipsum", e.message); 

There are two ways of writing test case

1. Annotate the test with the exception which is thrown by the method. Something like this @Test(expected = IndexOutOfBoundsException.class)

2. You can simply catch the exception in the test class using the try catch block and assert on the message that is thrown from the method in test class.

   try{ } catch(exception to be thrown from method e) { assertEquals("message", e.getmessage()); } 

I hope this answers your query Happy learning...

I wanted to comment with my solution to this problem, which avoided needing any of the exception related JUnit code.

I used assertTrue(boolean) combined with try/catch to look for my expected exception to be thrown. Here's an example:

public void testConstructor() { boolean expectedExceptionThrown; try { // Call constructor with bad arguments double a = 1; double b = 2; double c = a + b; // In my example, this is an invalid option for c new Triangle(a, b, c); expectedExceptionThrown = false; // because it successfully constructed the object } catch(IllegalArgumentException e) { expectedExceptionThrown = true; // because I'm in this catch block } catch(Exception e) { expectedExceptionThrown = false; // because it threw an exception but not the one expected } assertTrue(expectedExceptionThrown); }