Testing private methods (should you?) in JUnit - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a JUnit test method that tests a public method.

JUnit

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

class CalculatorTest {
    @Test
    void testAdd() {
        Calculator calc = new Calculator();
        int result = calc.add(2, 3);
        assertEquals([1], result);
    }
}

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

A6

B0

C23

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong expected value in assertEquals.

Confusing the order of parameters in assertEquals.

The add method should return the sum of 2 and 3, which is 5.

2fill in blank

medium

Complete the code to use reflection to access a private method named 'calculate' in a test.

JUnit

import org.junit.jupiter.api.Test;
import java.lang.reflect.Method;
import static org.junit.jupiter.api.Assertions.*;

class CalculatorTest {
    @Test
    void testPrivateCalculate() throws Exception {
        Calculator calc = new Calculator();
        Method method = Calculator.class.getDeclaredMethod("calculate", int.class, int.class);
        method.setAccessible(true);
        int result = (int) method.invoke(calc, 4, 5);
        assertEquals([1], result);
    }
}

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

A9

B20

C45

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Not setting the method accessible before invoking.

Using the wrong expected value in assertEquals.

The private method 'calculate' is expected to return the sum of 4 and 5, which is 9.

3fill in blank

hard

Fix the error in the test code that tries to test a private method directly.

JUnit

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

class CalculatorTest {
    @Test
    void testPrivateMethod() {
        Calculator calc = new Calculator();
        // This line causes a compile error because 'calculate' is private
        int result = calc.[1](3, 7);
        assertEquals(10, result);
    }
}

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

Acalculate

Bsubtract

Cadd

Dmultiply

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call private methods directly in test code.

Not understanding access modifiers in Java.

You cannot call a private method directly. Instead, test a public method like 'add' that uses the private method internally.

4fill in blank

hard

Fill both blanks to complete the explanation about testing private methods.

JUnit

/* It is generally recommended to test [1] methods instead of private methods directly.
 * Private methods should be tested indirectly through [2] methods.
 */

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

Apublic

Bprivate

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to test private methods directly.

Confusing public and private method roles.

Testing public methods ensures private methods are tested indirectly, keeping tests maintainable.

5fill in blank

hard

Fill all three blanks to complete the code snippet that uses reflection safely to test a private method.

JUnit

import org.junit.jupiter.api.Test;
import java.lang.reflect.Method;
import static org.junit.jupiter.api.Assertions.*;

class CalculatorTest {
    @Test
    void testPrivateMethodReflection() throws Exception {
        Calculator calc = new Calculator();
        Method method = Calculator.class.getDeclaredMethod("[1]", int.class, int.class);
        method.[2](true);
        int result = (int) method.invoke(calc, [3], 8);
        assertEquals(13, result);
    }
}

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

Acalculate

BsetAccessible

C5

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong method name.

Forgetting to set the method accessible.

Passing wrong argument values.

The private method 'calculate' is accessed by setting it accessible, then invoked with arguments 5 and 8.