Try/Catch fail

Using try/catch blocks with fail() calls to test for exceptions is an awkward outdated pattern. JUnit4 introduced the @Test(expected=...) annotation parameter to simplify this pattern, but it had its own limitations. An alternative @Rule ExpectedException approach was also available, but it was more verbose and more disconnected.

Before

TryCatchFailTest.java

import org.junit.jupiter.api.Test;

import static org.junit.jupiter.api.Assertions.assertTrue;
import static org.junit.jupiter.api.Assertions.fail;

class TryCatchFailTest {

    @Test
    void expectException() {
        try {
            boom();
            fail("Exception uncaught");
        } catch (IllegalStateException e) {
            // Catch before fail is called
        }
    }

    private void boom() {
        throw new IllegalStateException("boom!");
    }

    @Test
    void expectNoException() {
        try {
            noBoom();
            assertTrue(true, "No Exception");
        } catch (IllegalStateException e) {
            fail("Exception caught");
        }
    }

    private void noBoom() {
    }
}

warning

Using try/catch blocks with fail() calls is an outdated and less readable way to test for exceptions in JUnit 5. Instead, we should use the assertThatThrownBy() and assertDoesNotThrow methods, which are more concise and expressive.

After

TryCatchFailTest.java

import org.junit.jupiter.api.Test;

import static org.assertj.core.api.Assertions.assertThatThrownBy;
import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;

class TryCatchFailTest {

    @Test
    void expectException() {
        assertThatThrownBy(() -> boom()).isInstanceOf(IllegalStateException.class);
    }

    private void boom() {
        throw new IllegalStateException("boom!");
    }

    @Test
    void expectNoException() {
        assertDoesNotThrow(() -> noBoom(), "Exception caught");
    }

    private void noBoom() {
    }
}

tip

Both JUnit 5+ and AssertJ provide built-in methods to handle exception assertions, making tests cleaner and more maintainable.