Line and branch coverage in JUnit - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a JUnit test method that checks if the sum method returns the correct result.

JUnit

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

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

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

A5

B7

C4

D6

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong expected value in assertEquals.

Forgetting to import assertEquals.

The sum of 2 and 3 is 5, so the assertion should check for 5.

2fill in blank

medium

Complete the code to add a test method that checks if the isPositive method returns true for positive numbers.

JUnit

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

public class NumberTest {
    @Test
    public void testIsPositive() {
        NumberChecker checker = new NumberChecker();
        assertTrue(checker.isPositive([1]));
    }
}

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

A-5

B5

C-1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Testing with zero or negative numbers expecting true.

Not importing assertTrue.

The method isPositive should return true for positive numbers, so 5 is correct.

3fill in blank

hard

Fix the error in the test method to correctly check if the max method returns the larger number.

JUnit

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

public class MaxTest {
    @Test
    public void testMax() {
        MaxFinder finder = new MaxFinder();
        int max = finder.max(10, 20);
        assertEquals([1], max);
    }
}

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

A30

B10

C0

D20

Attempts:

3 left

💡 Hint

Common Mistakes

Using the smaller number as expected value.

Confusing the order of parameters.

The max method should return the larger number, which is 20 in this case.

4fill in blank

hard

Fill both blanks to complete the test method that checks if the isEven method returns true for even numbers and false for odd numbers.

JUnit

import static org.junit.jupiter.api.Assertions.assert[1];
import static org.junit.jupiter.api.Assertions.assertFalse;
import org.junit.jupiter.api.Test;

public class EvenOddTest {
    @Test
    public void testIsEven() {
        EvenOddChecker checker = new EvenOddChecker();
        assert[2](checker.isEven(4));
        assertFalse(checker.isEven(5));
    }
}

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

ATrue

BFalse

CEquals

DNull

Attempts:

3 left

💡 Hint

Common Mistakes

Using assertFalse instead of assertTrue for even number test.

Using assertEquals incorrectly here.

assertTrue is used to check if the method returns true for even numbers.

5fill in blank

hard

Fill all three blanks to complete the test method that verifies the behavior of the divide method, including handling division by zero.

JUnit

import static org.junit.jupiter.api.Assertions.assert[1];
import static org.junit.jupiter.api.Assertions.assertThrows;
import org.junit.jupiter.api.Test;

public class DivisionTest {
    @Test
    public void testDivide() {
        Calculator calc = new Calculator();
        assert[2](2, calc.divide(10, 5));
        assertThrows([3].class, () -> calc.divide(10, 0));
    }
}

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

AEquals

BassertEquals

CArithmeticException

DIllegalArgumentException

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong assertion method names.

Expecting wrong exception type for division by zero.

assertEquals checks the division result, and assertThrows expects an ArithmeticException for division by zero.

Practice

1. What does line coverage measure in JUnit testing?

easy

A. Whether the program runs without errors

B. Whether all possible input values are tested

C. Whether the test cases run in parallel

D. Whether each line of code is executed during tests

Solution

1. Step 1: Understand line coverage concept

   Line coverage measures if every line of code is executed at least once during testing.

2. Step 2: Compare with other options

   Options A, B, and D describe different testing aspects, not line coverage.

3. Final Answer:

   Whether each line of code is executed during tests -> Option D

4. Quick Check:

   Line coverage = executed lines [OK]

Hint: Line coverage = Did each line run? Check executed lines [OK]

Common Mistakes:

• Confusing line coverage with branch coverage
• Thinking line coverage checks input values
• Assuming line coverage means no errors

2. Which of the following is the correct JUnit annotation to mark a test method for coverage measurement?

easy

A. @Test

B. @Coverage

C. @RunCoverage

D. @Measure

Solution

1. Step 1: Recall JUnit test annotation

   The standard annotation to mark a test method in JUnit is @Test.

2. Step 2: Verify other options

   Annotations like @Coverage, @RunCoverage, and @Measure do not exist in JUnit.

3. Final Answer:

   @Test -> Option A

4. Quick Check:

   JUnit test method = @Test [OK]

Hint: JUnit test methods always use @Test annotation [OK]

Common Mistakes:

• Assuming coverage requires special annotation
• Using non-existent annotations
• Confusing coverage tools with JUnit annotations

3. Consider this Java method tested with JUnit:

public int max(int a, int b) {
  if (a > b) {
    return a;
  } else {
    return b;
  }
}

If your tests only call max(5, 3), what coverage is achieved?

medium

A. 100% line coverage, 100% branch coverage

B. 100% line coverage, 50% branch coverage

C. 50% line coverage, 100% branch coverage

D. 50% line coverage, 50% branch coverage

Solution

1. Step 1: Analyze lines executed by max(5, 3)

   Calling max(5, 3) executes the if condition and return a;, as well as the else block's closing brace, so all lines are executed, resulting in 100% line coverage.

2. Step 2: Analyze branches covered

   Only the 'if' branch (a > b true) is taken; the 'else' branch is not tested, so 50% branch coverage.

3. Final Answer:

   100% line coverage, 50% branch coverage -> Option B

4. Quick Check:

   One path = full line coverage, partial branch coverage [OK]

Hint: Test all if-else paths for full branch coverage [OK]

Common Mistakes:

• Thinking one test achieves 100% line coverage
• Confusing line coverage with branch coverage
• Ignoring else branch execution

4. You wrote tests for this method:

public boolean isPositive(int n) {
  if (n > 0) {
    return true;
  }
  return false;
}

But coverage report shows branch coverage less than 100%. What is the likely cause?

medium

A. Tests never call with n ≤ 0, missing else branch coverage

B. Tests have syntax errors causing incomplete runs

C. JUnit does not support branch coverage

D. Method has no branches to cover

Solution

1. Step 1: Identify branches in method

   The method has two branches: if (n > 0) true, else false.

2. Step 2: Understand branch coverage less than 100%

   If tests never call with n ≤ 0, the else branch is not executed, lowering branch coverage.

3. Final Answer:

   Tests never call with n ≤ 0, missing else branch coverage -> Option A

4. Quick Check:

   Branch coverage needs both if and else tested [OK]

Hint: Test both true and false conditions for full branch coverage [OK]

Common Mistakes:

• Assuming syntax errors cause coverage issues
• Believing JUnit lacks branch coverage support
• Ignoring else branch execution

5. Given this method:

public int classify(int x) {
  if (x > 0) {
    if (x % 2 == 0) {
      return 1;
    } else {
      return 2;
    }
  } else {
    return 3;
  }
}

What is the minimum number of JUnit test cases needed to achieve 100% line and branch coverage?

hard

A. 4

B. 2

C. 3

D. 5

Solution

1. Step 1: Identify branches

   There are three branches: outer if (x > 0) true and false, and inner if (x % 2 == 0) true and false.

2. Step 2: Determine test cases to cover all branches

   Tests needed: one with x > 0 and even (return 1), one with x > 0 and odd (return 2), and one with x ≤ 0 (return 3).

3. Final Answer:

   3 -> Option C

4. Quick Check:

   Three tests cover all branches and lines [OK]

Hint: Cover all if-else paths with minimal tests [OK]

Common Mistakes:

• Thinking two tests cover all branches
• Ignoring nested if branches
• Overestimating tests needed