How Does JUnit 5\'s `assertThrows()` Simplify Exception Assertion Testing?

Exceptional Exception Assertions in JUnit 5

In JUnit 5, asserting that a method throws an exception has been simplified with the introduction of assertThrows(). This method provides a more concise and convenient way to verify exception behavior, particularly when multiple exceptions are expected within the same test.

Previously, developers relied on the @Rule annotation to check for exceptions, but this approach had limitations when multiple exceptions were involved. assertThrows(), on the other hand, allows for flexible and customizable exception testing.

By leveraging Java 8 lambdas, assertThrows() enables developers to write concise and expressive test assertions:

import static org.junit.jupiter.api.Assertions.assertThrows;

@Test
void exceptionTesting() {
    MyException thrown = assertThrows(
        MyException.class,
        () -> myObject.doThing(),
        "Expected doThing() to throw, but it didn't"
    );

    assertTrue(thrown.getMessage().contains("Stuff"));
}

In this example, assertThrows() is used to check if the doThing() method throws a MyException when invoked. The lambda expression passed as the second argument defines the code that is expected to throw the exception. The third argument provides an optional message to be displayed in case the assertion fails.

By using assertThrows(), developers can streamline their exception testing code, easily assert multiple exceptions within a single test, and provide clear and informative error messages when assertions fail.

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