assertTrue and assertFalse in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ assertion

intermediate

Using assertTrue with a boolean expression

Which assertion correctly verifies that the variable isActive is true?

JUnit

boolean isActive = (5 > 3);

A assertTrue(isActive);

B assertTrue(isActive == false);

C assertFalse(isActive);

D assertFalse(!isActive);

💡 Hint

Remember, assertTrue expects the condition to be true.

assertTrue(isActive); passes because isActive is true. Other options either check for false or negate the condition incorrectly.

❓ assertion

intermediate

Using assertFalse with a boolean expression

Which assertion correctly verifies that the variable isEmpty is false?

JUnit

boolean isEmpty = ("text".isEmpty());

A assertTrue(isEmpty);

B assertFalse(!isEmpty);

C assertFalse(isEmpty);

D assertTrue(!isEmpty);

💡 Hint

assertFalse expects the condition to be false.

assertFalse(isEmpty); passes because isEmpty is false. Option C is logically correct but uses assertTrue, not assertFalse.

❓ Predict Output

advanced

What happens when assertTrue fails?

Consider the following JUnit test method. What is the test result when it runs?

JUnit

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

import org.junit.jupiter.api.Test;

@Test
void testFail() {
    assertTrue(2 + 2 == 5);
}

A Test is skipped automatically.

B Test passes successfully.

C Test fails with a NullPointerException.

D Test fails with an AssertionError.

💡 Hint

assertTrue expects the condition to be true.

The condition 2 + 2 == 5 is false, so assertTrue throws an AssertionError causing the test to fail.

🔧 Debug

advanced

Identify the incorrect assertion usage

Which option contains an incorrect use of assertFalse that will cause a compilation error?

JUnit

boolean flag = true;

A assertFalse(!flag);

B assertFalse();

C assertFalse(flag);

D assertFalse(flag == false);

💡 Hint

Check the method parameters required by assertFalse.

assertFalse() without any argument causes a compilation error because it requires a boolean parameter.

🧠 Conceptual

expert

Choosing between assertTrue and assertFalse for readability

Given a boolean variable isValid, which assertion improves test readability best when checking that isValid is false?

A assertFalse(isValid);

B assertTrue(isValid == false);

C assertTrue(!isValid);

D assertFalse(!isValid);

💡 Hint

Choose the assertion that directly expresses the expected condition.

assertFalse(isValid); clearly states the expectation that isValid should be false, improving readability over negations.