junit test method with exception code example

Example 1: junit 5 assert exception message

Throwable exceptionThatWasThrown = assertThrows(NullPointerException.class, () -> {
    codeThatThrows;
});

assertThat(exceptionThatWasThrown.getMessage(), equalTo("Message I expected to be thrown"));

Example 2: how to assert that an exception is thrown java

@Test
public void whenExceptionThrown_thenAssertionSucceeds() {
    Exception exception = assertThrows(NumberFormatException.class, () -> {
        Integer.parseInt("1a");
    });

    String expectedMessage = "For input string";
    String actualMessage = exception.getMessage();

    assertTrue(actualMessage.contains(expectedMessage));
}