In Java, What Is The Method To Ensure That A Specific Exception Is Thrown In JUnit Tests?

To assert that a certain exception is thrown in JUnit tests, you can use the @Test annotation along with the expected attribute. Here’s an example:

import org.junit.Test;

public class MyTestClass {

    @Test(expected = MyException.class)
    public void myTestMethod() {
        // Code that is expected to throw MyException
    }
}

In the above example, when running the myTestMethod test, if the code within the method throws a MyException or its subclass, the test will pass. If any other exception is thrown or no exception is thrown at all, the test will fail.

Note that this method is suitable for cases where you don’t need to examine the specific content of the exception. If you need to inspect the exception further, you can use the ExpectedException rule or the assertThrows method.

Using the ExpectedException rule:

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

public class MyTestClass {
    
    @Rule
    public ExpectedException exception = ExpectedException.none();
    
    @Test
    public void myTestMethod() {
        exception.expect(MyException.class);
        exception.expectMessage("Expected error message"); // optional
        
        // Code that is expected to throw MyException with the specified error message
    }
}

Using the assertThrows method:

import org.junit.Test;
import static org.junit.Assert.assertThrows;

public class MyTestClass {
    
    @Test
    public void myTestMethod() {
        assertThrows(MyException.class, () -> {
            // Code that is expected to throw MyException
        });
    }
}

Both the ExpectedException rule and assertThrows method allow you to provide additional assertions on the exception itself, such as checking specific error messages or inspecting properties of the exception object.

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