JUnit Assert Exception

Ccentron Redaktion · March 2024 ·2 min read ·JavaScript, Tutorial

We can test expected exceptions using JUnit 5 assertThrows assertion. This JUnit assertion method returns the thrown exception, so we can use it to assert exception message too.

Here is a simple example showing how to assert exception in JUnit 5.

Code

String str = null;
assertThrows(NullPointerException.class, () -> str.length());

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JUnit 5 Assert Exception Message

Let’s say we have a class defined as:

Code

class Foo {
    void foo() throws Exception {
        throw new Exception("Exception Message");
    }
}

Let’s see how we can test exception as well as its message.

Code

Foo foo = new Foo();
Exception exception = assertThrows(Exception.class, () -> foo.foo());
assertEquals("Exception Message", exception.getMessage());

JUnit 4 Expected Exception

We can use JUnit 4 @Test annotation expected attribute to define the expected exception thrown by the test method.

Code

@Test(expected = Exception.class)
public void test() throws Exception {
    Foo foo = new Foo();
    foo.foo();
}

JUnit 4 Assert Exception Message

If we want to test exception message, then we will have to use ExpectedException rule. Below is a complete example showing how to test exception as well as exception message.

package com.journaldev.junit4;

import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.ExpectedException;

public class JUnit4TestException {

    @Rule
    public ExpectedException thrown = ExpectedException.none();

    @Test
    public void test1() throws Exception {
        Foo foo = new Foo();
        thrown.expect(Exception.class);
        thrown.expectMessage("Exception Message");
        foo.foo();
    }
}

That’s all for a quick roundup on testing expected exceptions in JUnit 5 and JUnit 4.

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JUnit Assert Exception - JUnit 5 and JUnit 4