junit testing - assertEquals for exception

Question

How can I use assertEquals to see if the exception message is correct? The test passes but I don\'t know if it hits the correct error or not.

The test I am running.

Answer 1

try {
    assertEquals("Legal Values: Package Type must be P or R", Shipping.shippingCost('P', -5));
    Assert.fail( "Should have thrown an exception" );
} 
catch (Exception e) {
    String expectedMessage = "this is the message I expect to get";
    Assert.assertEquals( "Exception message must be correct", expectedMessage, e.getMessage() );
}