assertDoesNotThrow in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the result of this JUnit test using assertDoesNotThrow?

Consider the following JUnit test method. What will be the test execution result?

JUnit

import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
import org.junit.jupiter.api.Test;

public class SampleTest {
    @Test
    void testNoException() {
        assertDoesNotThrow(() -> {
            int a = 5;
            int b = 10;
            int c = a + b;
        });
    }
}

A Test passes because no exception is thrown inside the lambda.

B Test fails due to a compilation error in the lambda expression.

C Test fails because an exception is thrown inside the lambda.

D Test passes but with a warning about unused variables.

💡 Hint

assertDoesNotThrow expects the lambda to run without exceptions.

The lambda inside assertDoesNotThrow runs code that does not throw any exceptions, so the test passes.

❓ assertion

intermediate

Which assertion correctly uses assertDoesNotThrow to check a method that might throw?

You have a method that might throw an IOException. Which assertion correctly tests that it does NOT throw any exception?

JUnit

void riskyMethod() throws IOException {
    // might throw IOException
}

A assertDoesNotThrow(riskyMethod());

B assertDoesNotThrow(() -> riskyMethod());

C assertDoesNotThrow(() -> { riskyMethod(); return null; });

D assertDoesNotThrow(() -> riskyMethod() throws IOException);

💡 Hint

assertDoesNotThrow expects a lambda expression or executable.

Option B correctly passes a lambda that calls riskyMethod. Option B calls the method immediately, causing a compile error. Option B returns null unnecessarily but compiles. Option B is invalid syntax.

🔧 Debug

advanced

Why does this assertDoesNotThrow test fail?

Examine the following test code and identify why the test fails.

JUnit

assertDoesNotThrow(() -> {
    throw new Exception("Error");
});

A The syntax of the lambda is incorrect; it needs a return statement.

B assertDoesNotThrow cannot accept lambdas that throw any exceptions.

C The lambda throws a checked Exception, causing the test to fail.

D The Exception class is not imported, causing a compile error.

💡 Hint

assertDoesNotThrow fails if the lambda throws an exception.

The lambda throws a checked Exception, causing assertDoesNotThrow to fail the test.

🧠 Conceptual

advanced

What is the main purpose of assertDoesNotThrow in JUnit tests?

Choose the best description of what assertDoesNotThrow verifies in a test.

A It verifies that the tested code runs without throwing any exceptions.

B It verifies that the tested code throws a specific exception.

C It verifies that the tested code returns a non-null value.

D It verifies that the tested code completes within a time limit.

💡 Hint

Think about what 'does not throw' means.

assertDoesNotThrow checks that no exceptions are thrown during execution of the tested code.

❓ framework

expert

Which option correctly captures the return value when using assertDoesNotThrow?

You want to test a method that returns a value and ensure it does not throw an exception. How do you capture the return value using assertDoesNotThrow?

JUnit

public String getData() throws Exception {
    return "data";
}

A assertDoesNotThrow(() -> { return getData(); });

B String result = assertDoesNotThrow(getData());

C String result = assertDoesNotThrow(() -> { getData(); });

D String result = assertDoesNotThrow(() -> getData());

💡 Hint

assertDoesNotThrow returns the value from the lambda if no exception occurs.

Option D correctly assigns the returned value from assertDoesNotThrow. Option D is invalid syntax. Option D does not assign the return value. Option D returns void lambda, so cannot assign.