JUnit5 assertNull() Example

Hey guys in this post, we will discuss the Junit5 assertNull() method with easy to understanding example

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Overview

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JUnit5 provides the assertNull() method, it asserts that the object is null. There are many overloaded assertNull() methods available. Below is just a sample screenshot for your reference.

Example

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Consider the following method for checking the null value.

package in.bushansirgur.main;

public class MyUtils {
	
	public Object checkNull(Object object) {
		if (object != null) {
			return object;
		}
		return null;
	}
}

JUnit5 Success Test Case

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Now we want to write a JUnit5 test case for the above method, we can use the assertNull() method to assert that the object is null

package in.bushansirgur.main;

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

import org.junit.jupiter.api.Test;

class MyUtilsTest {
	
	@Test
	void testNull() {
		MyUtils myUtils = new MyUtils();
		assertNull(myUtils.checkNull(null), () -> "It should be null");
	}

}

When we run the test case, we should see a green bar indicating that the test case passed.

JUnit5 Failure Test Case

---

Now if anyone changes the implementation/logic then the test case should fail. Let’s change the method implementation with the following code –

package in.bushansirgur.main;

public class MyUtils {
	
	public Object checkNull(Object object) {
		if (object != null) {
			return object;
		}
		return "";
	}
}

Now when we run the test case, we should see a red bar indicating that the test case failed.

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