assertEquals in JUnit - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ assertion

intermediate

Understanding assertEquals with primitive types

What will be the result of this JUnit assertion?

assertEquals(5, 2 + 3);

JUnit

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

public class TestClass {
    @org.junit.jupiter.api.Test
    void testSum() {
        assertEquals(5, 2 + 3);
    }
}

A Test fails because assertEquals expects strings

B Test passes because 2 + 3 equals 5

C Test fails due to a compilation error

D Test passes but with a warning about types

💡 Hint

assertEquals compares expected and actual values for equality.

The assertion compares the expected value 5 with the actual result of 2 + 3, which is also 5, so the test passes.

❓ assertion

intermediate

assertEquals with String objects

What will happen when this assertion runs?

assertEquals("hello", "he" + "llo");

JUnit

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

public class TestClass {
    @org.junit.jupiter.api.Test
    void testStringConcat() {
        assertEquals("hello", "he" + "llo");
    }
}

A Test passes because the strings are equal in content

B Test fails because the strings are different objects

C Test fails due to a NullPointerException

D Test passes but only if using assertSame instead

💡 Hint

assertEquals compares string content, not object references.

assertEquals checks if the string contents are equal, which they are, so the test passes.

❓ assertion

advanced

assertEquals with floating point numbers and delta

What is the result of this assertion?

assertEquals(0.3, 0.1 + 0.2, 0.0001);

JUnit

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

public class TestClass {
    @org.junit.jupiter.api.Test
    void testFloatingPoint() {
        assertEquals(0.3, 0.1 + 0.2, 0.0001);
    }
}

A Test passes because the difference is within the delta

B Test fails because floating point addition is exact

C Test fails due to a compilation error missing delta

D Test passes but delta should be zero for exact match

💡 Hint

Floating point arithmetic can have small precision errors; delta allows tolerance.

The sum 0.1 + 0.2 is approximately 0.30000000000000004, which is within the delta 0.0001, so the test passes.

❓ assertion

advanced

assertEquals with arrays

What will happen when this assertion runs?

assertEquals(new int[]{1, 2}, new int[]{1, 2});

JUnit

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

public class TestClass {
    @org.junit.jupiter.api.Test
    void testArrayEquals() {
        assertEquals(new int[]{1, 2}, new int[]{1, 2});
    }
}

A Test passes only if using assertArrayEquals instead

B Test passes because arrays have the same contents

C Test fails due to NullPointerException

D Test fails because assertEquals compares array references, not contents

💡 Hint

assertEquals on arrays compares references, not contents.

assertEquals compares object references for arrays, so two different arrays with same contents fail the test.

❓ assertion

expert

assertEquals with custom objects and equals method

Given this class:

public class Person {
    String name;
    public Person(String name) { this.name = name; }
}

What will happen when this assertion runs?

assertEquals(new Person("Alice"), new Person("Alice"));

JUnit

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

public class TestClass {
    public static class Person {
        String name;
        public Person(String name) { this.name = name; }
    }

    @org.junit.jupiter.api.Test
    void testPersonEquals() {
        assertEquals(new Person("Alice"), new Person("Alice"));
    }
}

A Test passes because names are equal

B Test fails due to NullPointerException

C Test fails because Person does not override equals method

D Test passes only if Person overrides hashCode

💡 Hint

Default equals compares object references unless overridden.

Without overriding equals, two different Person objects are not equal even if their fields match, so the test fails.