Exceptions
The JUnit 4 way of testing exceptions involved adding expected to the @Test annotation, and allowing the exception to be thrown from the test method.
@Test(expected=Exception.class)
public void test_withdrawException_throws_Exception_for_negative_input() throws Exception {
Account a = new Account(100.0);
a.withdrawException(-0.01);
}
The exception is thrown by withdrawException so JUnit can catch it.
assertThrows to Test Exceptions¶
We can now keep the testing contained in our method with assertThrows.
Throwable assertThrows(Class exceptionType, Executable) - assert that exceptionType was thrown, and return it as a Throwable.
* Returning a Throwable allows us to examine it.
We place our method call in an Executable implemented with a lambda expression.
@Test
@DisplayName("withDrawException throws Exception for negative input")
public void testException() {
Account a = new Account(100.0);
Exception e = assertThrows(Exception.class, // expected type
() -> a.withdrawException(-0.01) ); // lambda Executable
// examine the Exception
assertEquals("Amount cannot be less than zero.", e.getMessage());
}