assertEquals in JUnit - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if the expected value equals the actual value using JUnit.

JUnit

assertEquals([1], actualValue);

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

A"expected"

BactualValue

CexpectedValue

Dresult

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the actual value as the first argument instead of the expected value.

Using a variable that is not defined.

The assertEquals method compares the expected value to the actual value. The first argument should be the expected value.

2fill in blank

medium

Complete the code to assert that two strings are equal in a JUnit test.

JUnit

assertEquals([1], "Hello World");

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

A"World"

B"Hello World"

C"Hello"

D"hello world"

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string with different case or spelling.

Swapping expected and actual values.

The expected string must exactly match the actual string for assertEquals to pass.

3fill in blank

hard

Fix the error in the assertion to correctly compare two integers.

JUnit

assertEquals([1], 5);

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

A5

B"5"

Cfive

D5.0

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string "5" instead of integer 5.

Using a floating point number 5.0.

The expected value must be an integer 5, not a string or float, to match the actual integer value.

4fill in blank

hard

Fill both blanks to assert that the method returns the expected boolean value.

JUnit

assertEquals([1], [2]);

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

Atrue

Bfalse

CisValid()

DcheckResult()

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping expected and actual values.

Using a method that does not return a boolean.

The expected value is true and the actual value is the result of isValid() method.

5fill in blank

hard

Fill all three blanks to assert that the method returns the expected string with a custom failure message.

JUnit

assertEquals([1], [2], [3]);

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

A"Expected greeting did not match"

BgetGreeting()

C"Hello, Tester!"

D"Greeting mismatch"

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the message in the wrong position.

Swapping expected and actual values.

The first blank is the failure message, the second is the expected string, and the third is the actual method call.

Practice

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

easy

A. To check if two values are equal and fail the test if not

B. To print values during test execution

C. To skip a test case

D. To create a new test method

Solution

1. Step 1: Understand the role of assertEquals

   assertEquals compares two values: expected and actual.

2. Step 2: Identify the test behavior

   If the values differ, the test fails, helping find bugs.

3. Final Answer:

   To check if two values are equal and fail the test if not -> Option A

4. Quick Check:

   assertEquals checks equality [OK]

Hint: assertEquals fails test if values differ [OK]

Common Mistakes:

• Thinking assertEquals prints output
• Confusing assertEquals with skipping tests
• Using assertEquals to create tests

2. Which of the following is the correct syntax for assertEquals with a message in JUnit?

easy

A. assertEquals("Error message", expected, actual);

B. assertEquals(actual, expected, "Error message");

C. assertEquals(expected, actual, "Error message");

D. assertEquals("Error message", actual, expected);

Solution

1. Step 1: Recall assertEquals method signature with message

   The correct order is: message, expected, actual.

2. Step 2: Match options with correct order

   assertEquals("Error message", expected, actual); matches this order exactly.

3. Final Answer:

   assertEquals("Error message", expected, actual); -> Option A

4. Quick Check:

   Message first, then expected, actual [OK]

Hint: Message comes first in assertEquals with message [OK]

Common Mistakes:

• Swapping expected and actual parameters
• Placing message last instead of first
• Using actual before expected

3. What will happen when this JUnit test runs?

int expected = 5;
int actual = 3 + 2;
assertEquals(expected, actual);

medium

A. Compilation error due to wrong assertEquals usage

B. Test fails because expected does not equal actual

C. Test passes because expected equals actual

D. Test is skipped automatically

Solution

1. Step 1: Calculate actual value

   3 + 2 equals 5, so actual is 5.

2. Step 2: Compare expected and actual

   Both expected and actual are 5, so assertEquals passes.

3. Final Answer:

   Test passes because expected equals actual -> Option C

4. Quick Check:

   5 equals 5 means pass [OK]

Hint: Calculate actual before comparing [OK]

Common Mistakes:

• Assuming 3 + 2 is not 5
• Confusing expected and actual values
• Thinking assertEquals causes compilation error here

4. Identify the error in this JUnit assertion:

assertEquals(5, "5");

medium

A. Runtime exception thrown

B. No error, test passes

C. Compilation error due to wrong parameter order

D. Test fails because int and String types differ

Solution

1. Step 1: Check parameter types

   First is int 5, second is String "5".

2. Step 2: Understand assertEquals behavior with different types

   assertEquals compares values and types; int and String differ, so test fails.

3. Final Answer:

   Test fails because int and String types differ -> Option D

4. Quick Check:

   Different types cause failure [OK]

Hint: Types must match for assertEquals to pass [OK]

Common Mistakes:

• Assuming int 5 equals String "5"
• Thinking parameter order is wrong here
• Expecting compilation or runtime error

5. You want to test a method that returns a list of strings. Which assertEquals usage **including a custom error message** correctly checks if the returned list matches List.of("a", "b")?

List<String> expected = List.of("a", "b");
List<String> actual = myMethod();

hard

A. assertEquals(expected, actual);

B. assertEquals("Lists differ", expected, actual);

C. assertEquals(expected.size(), actual.size());

D. assertEquals(expected.toString(), actual.toString());

Solution

1. Step 1: Understand assertEquals for lists

   assertEquals compares lists by content if types match.

2. Step 2: Check options for best practice

   assertEquals("Lists differ", expected, actual); adds a helpful message and uses correct parameter order.

3. Final Answer:

   assertEquals("Lists differ", expected, actual); -> Option B

4. Quick Check:

   Message first, then expected and actual [OK]

Hint: Use message first with expected, actual for clarity [OK]

Common Mistakes:

• Comparing string representations instead of lists
• Only comparing list sizes
• Omitting message for clarity