Testing Expected Exceptions in JUnit
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.
JUnit Assert Exception
Here is a simple example showing how to assert exception in JUnit 5.
String str = null;
assertThrows(NullPointerException.class, () -> str.length());
JUnit 5 Assert Exception Message
Let’s say we have a class defined as:
class Foo {
void foo() throws Exception {
throw new Exception("Exception Message");
}
}
Let’s see how we can test exception as well as its message.
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.
@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.
