assertDoesNotThrow in JUnit - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check that the method does not throw any exception.

JUnit

assertDoesNotThrow(() -> [1]());

Drag options to blanks, or click blank then click option'

AfailTest

BthrowException

CmyMethod

DnullPointer

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method that actually throws an exception.

Not using a lambda expression.

Calling the method outside the lambda.

The assertDoesNotThrow method expects a lambda that calls the method under test. Here, myMethod is the method that should not throw an exception.

2fill in blank

medium

Complete the code to assert that the lambda expression does not throw an exception.

JUnit

assertDoesNotThrow([1]);

Drag options to blanks, or click blank then click option'

A() -> myMethod()

B() -> throwException()

CmyMethod()

DthrowException()

Attempts:

3 left

💡 Hint

Common Mistakes

Passing a method call directly instead of a lambda.

Using a method that throws an exception inside the lambda.

The argument to assertDoesNotThrow must be a lambda expression. Here, () -> myMethod() is the correct lambda that calls myMethod without throwing exceptions.

3fill in blank

hard

Fix the error in the assertion to correctly check no exception is thrown.

JUnit

assertDoesNotThrow(() -> [1]);

Drag options to blanks, or click blank then click option'

AmyMethod()

BmyMethod

CthrowException()

DthrowException

Attempts:

3 left

💡 Hint

Common Mistakes

Using method reference without parentheses inside the lambda.

Calling a method that throws an exception.

The lambda must call the method with parentheses to execute it. Using myMethod() calls the method inside the lambda, which is correct.

4fill in blank

hard

Fill both blanks to assert no exception is thrown when calling the method with arguments.

JUnit

assertDoesNotThrow(() -> [1]([2]));

Drag options to blanks, or click blank then click option'

AprocessData

B"input"

C42

DthrowException

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method that throws an exception.

Passing an argument that is not a string literal.

The lambda calls processData with the string argument "input". This checks that calling processData("input") does not throw an exception.

5fill in blank

hard

Fill all three blanks to assert no exception is thrown when calling a method with two arguments.

JUnit

assertDoesNotThrow(() -> [1]([2], [3]));

Drag options to blanks, or click blank then click option'

AcalculateSum

B5

C10

DthrowException

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method that throws exceptions.

Passing arguments in the wrong order.

The lambda calls calculateSum with arguments 5 and 10. This asserts that calling calculateSum(5, 10) does not throw an exception.

Practice

1. What is the main purpose of assertDoesNotThrow in JUnit testing?

easy

A. To assert that a method returns a specific value

B. To check that a block of code runs without throwing any exceptions

C. To verify that a specific exception is thrown by the code

D. To measure the execution time of a code block

Solution

1. Step 1: Understand the purpose of assertDoesNotThrow

   This assertion is designed to confirm that no exceptions occur when running a code block.

2. Step 2: Compare with other assertions

   Unlike assertions that check for exceptions or return values, assertDoesNotThrow ensures smooth execution without errors.

3. Final Answer:

   To check that a block of code runs without throwing any exceptions -> Option B

4. Quick Check:

   assertDoesNotThrow means no exceptions thrown [OK]

Hint: Remember: assertDoesNotThrow means code runs without errors [OK]

Common Mistakes:

• Confusing assertDoesNotThrow with assertThrows
• Thinking it checks return values
• Assuming it measures performance

2. Which of the following is the correct syntax to use assertDoesNotThrow in JUnit 5?

easy

A. assertDoesNotThrow(methodToTest());

B. assertDoesNotThrow { methodToTest() };

C. assertDoesNotThrow(() -> methodToTest());

D. assertDoesNotThrow(methodToTest);

Solution

1. Step 1: Recall the lambda syntax for assertDoesNotThrow

   assertDoesNotThrow expects a lambda expression or executable block, written as () -> methodToTest().

2. Step 2: Identify incorrect options

   Options A, C, and D use incorrect syntax: A calls the method directly, C uses braces like other languages, D passes method reference without lambda.

3. Final Answer:

   assertDoesNotThrow(() -> methodToTest()); -> Option C

4. Quick Check:

   Use lambda () -> method() with assertDoesNotThrow [OK]

Hint: Use lambda syntax () -> method() inside assertDoesNotThrow [OK]

Common Mistakes:

• Calling the method directly inside assertDoesNotThrow
• Using curly braces instead of lambda arrows
• Passing method name without parentheses or lambda

3. What will be the result of this JUnit test?

assertDoesNotThrow(() -> { int x = 5 / 1; });

medium

A. Test fails due to syntax error

B. Test fails due to ArithmeticException

C. Test fails due to NullPointerException

D. Test passes because no exception is thrown

Solution

1. Step 1: Analyze the code inside assertDoesNotThrow

   The code divides 5 by 1, which is valid and does not throw any exception.

2. Step 2: Understand assertDoesNotThrow behavior

   Since no exception occurs, the assertion passes and the test succeeds.

3. Final Answer:

   Test passes because no exception is thrown -> Option D

4. Quick Check:

   Division by 1 is safe, so no exception [OK]

Hint: Check if code inside lambda throws exception or not [OK]

Common Mistakes:

• Assuming division always throws exception
• Confusing ArithmeticException with other exceptions
• Thinking assertDoesNotThrow checks return values

4. Identify the error in this JUnit test using assertDoesNotThrow:

assertDoesNotThrow(() -> { int y = 10 / 0; });

medium

A. ArithmeticException will cause test to fail

B. No error; test will pass

C. Syntax error due to missing semicolon

D. NullPointerException will cause test to fail

Solution

1. Step 1: Examine the code inside assertDoesNotThrow

   The code divides 10 by 0, which causes an ArithmeticException at runtime.

2. Step 2: Understand assertDoesNotThrow behavior on exceptions

   assertDoesNotThrow expects no exceptions; if one occurs, the test fails.

3. Final Answer:

   ArithmeticException will cause test to fail -> Option A

4. Quick Check:

   Division by zero throws ArithmeticException [OK]

Hint: Division by zero throws exception, so test fails [OK]

Common Mistakes:

• Thinking test passes despite exception
• Confusing exception types
• Ignoring runtime exceptions inside lambda

5. You want to test a method processData() that may throw a checked exception. How do you use assertDoesNotThrow to verify it runs without exceptions?

hard

A. assertDoesNotThrow(() -> processData());

B. assertDoesNotThrow(processData());

C. assertDoesNotThrow(() -> { try { processData(); } catch(Exception e) {} });

D. assertDoesNotThrow(() -> { processData() });

Solution

1. Step 1: Understand handling checked exceptions in lambdas

   assertDoesNotThrow accepts an Executable, whose execute() method throws Throwable, so checked exceptions are permitted in the lambda.

2. Step 2: Identify the correct lambda syntax

   The standard syntax is a concise lambda: () -> processData().

3. Step 3: Evaluate options

   A: correct single-expression lambda. B: direct method call without lambda. C: catches exceptions inside lambda, hiding potential failures. D: syntax error due to missing semicolon after processData() in the block lambda.

4. Final Answer:

   assertDoesNotThrow(() -> processData()); -> Option A

5. Quick Check:

   Lambda () -> processData() handles checked exceptions correctly [OK]

Hint: Use lambda syntax () -> processData() inside assertDoesNotThrow [OK]

Common Mistakes:

• Calling method directly without lambda
• Syntax errors like missing semicolon in block lambdas
• Catching exceptions inside lambda hiding test failures