Coverage thresholds in JUnit - Test Execution Trace

Test Overview

This test runs unit tests and checks if the code coverage meets the minimum required thresholds for instructions, branches, and lines. It verifies that the coverage is above the set limits to ensure good test quality.

Test Code - JUnit 5

JUnit

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

public class CoverageThresholdTest {

    @Test
    void sampleTest() {
        int result = add(2, 3);
        assertEquals(5, result);
    }

    int add(int a, int b) {
        return a + b;
    }

    // Note: Coverage thresholds are usually configured in build tools like Maven or Gradle,
    // but here we simulate a check by asserting coverage values.

    @Test
    void coverageThresholdCheck() {
        // Simulated coverage values (in percent)
        int instructionCoverage = 85;
        int branchCoverage = 80;
        int lineCoverage = 90;

        int minInstructionCoverage = 80;
        int minBranchCoverage = 75;
        int minLineCoverage = 85;

        assertTrue(instructionCoverage >= minInstructionCoverage, "Instruction coverage below threshold");
        assertTrue(branchCoverage >= minBranchCoverage, "Branch coverage below threshold");
        assertTrue(lineCoverage >= minLineCoverage, "Line coverage below threshold");
    }
}

Execution Trace - 4 Steps

Step	Action	System State	Assertion	Result
1	Test runner starts and loads CoverageThresholdTest class	JUnit test environment initialized	—	PASS
2	Runs sampleTest method	Method add(2,3) returns 5	assertEquals(5, result)	PASS
3	Runs coverageThresholdCheck method	Simulated coverage values: instruction=85%, branch=80%, line=90%	assertTrue(instructionCoverage >= 80), assertTrue(branchCoverage >= 75), assertTrue(lineCoverage >= 85)	PASS
4	Test runner completes all tests	All tests passed	—	PASS

Failure Scenario

Failing Condition: One or more coverage values are below the minimum thresholds

Execution Trace Quiz - 3 Questions

What does the coverageThresholdCheck test verify?

A That the test runner starts correctly

B That the add method returns correct sums

C That code coverage percentages meet minimum required thresholds

D That the coverage tool is installed

Key Result

Setting coverage thresholds helps maintain good test quality by ensuring enough code is tested, preventing unnoticed bugs.

Practice

1. What is the main purpose of setting coverage thresholds in JUnit testing?

easy

A. To automatically fix bugs in the code

B. To speed up test execution time

C. To ensure a minimum percentage of code is tested

D. To generate user interface reports

Solution

1. Step 1: Understand coverage thresholds

   Coverage thresholds define the minimum amount of code that must be tested to pass.

2. Step 2: Identify the main goal

   The goal is to keep tests thorough by enforcing minimum test coverage.

3. Final Answer:

   To ensure a minimum percentage of code is tested -> Option C

4. Quick Check:

   Coverage thresholds = minimum tested code [OK]

Hint: Coverage thresholds set minimum tested code percentage [OK]

Common Mistakes:

• Thinking thresholds speed up tests
• Believing thresholds fix bugs automatically
• Confusing thresholds with report generation

2. Which of the following is the correct way to set a line coverage threshold of 80% using JaCoCo in a Maven pom.xml?

easy

A. <rule><limit><counter>LINE</counter><value>COVEREDRATIO</value><minimum>0.8</minimum></limit></rule>

B. <rule><limit><counter>LINE</counter><value>MISSEDCOUNT</value><maximum>0.8</maximum></limit></rule>

C. <rule><limit><counter>BRANCH</counter><value>COVEREDRATIO</value><minimum>80</minimum></limit></rule>

D. <rule><limit><counter>LINE</counter><value>COVEREDCOUNT</value><minimum>0.8</minimum></limit></rule>

Solution

1. Step 1: Identify correct counter and value

   For line coverage, the counter is LINE and the value to check coverage ratio is COVEREDRATIO.

2. Step 2: Check threshold value format

   Minimum coverage is set as a decimal ratio (0.8 for 80%).

3. Final Answer:

   Rule with LINE counter, COVEREDRATIO value, and minimum 0.8 -> Option A

4. Quick Check:

   Line coverage threshold = 0.8 COVEREDRATIO [OK]

Hint: Use LINE + COVEREDRATIO + minimum 0.8 for 80% threshold [OK]

Common Mistakes:

• Using MISSEDCOUNT instead of COVEREDRATIO
• Setting minimum as 80 instead of 0.8
• Confusing BRANCH counter with LINE

3. Given the following JaCoCo coverage report snippet:

{"LINE": {"covered": 40, "missed": 10}}

What is the line coverage ratio, and does it meet a threshold of 85%?

medium

A. Coverage is 75%, which does not meet the 85% threshold

B. Coverage is 75%, which meets the 85% threshold

C. Coverage is 80%, which meets the 85% threshold

D. Coverage is 80%, which does not meet the 85% threshold

Solution

1. Step 1: Calculate coverage ratio

   Total lines = covered + missed = 40 + 10 = 50. Coverage ratio = 40 / 50 = 0.8 or 80%.

2. Step 2: Compare with threshold

   Threshold is 85%, coverage is 80%, so coverage does not meet threshold.

3. Final Answer:

   Coverage is 80%, which does not meet the 85% threshold -> Option D

4. Quick Check:

   40/50 = 0.8 < 0.85 [OK]

Hint: Divide covered by total lines, compare to threshold [OK]

Common Mistakes:

• Adding covered and missed incorrectly
• Confusing coverage percentage with missed percentage
• Assuming 80% meets 85% threshold

4. You set a branch coverage threshold of 90% in your JaCoCo config, but the build passes even when coverage is 85%. What is the most likely cause?

medium

A. The JaCoCo plugin is not configured to fail the build on threshold violation

B. The threshold value is set as maximum instead of minimum

C. Branch coverage cannot be enforced with JaCoCo

D. The threshold is set on LINE coverage, not BRANCH coverage

Solution

1. Step 1: Understand threshold enforcement

   Thresholds require configuration to fail the build if coverage is below minimum.

2. Step 2: Identify common misconfiguration

   If the build passes despite low coverage, likely the fail-on-violation setting is missing or disabled.

3. Final Answer:

   JaCoCo plugin not configured to fail build on threshold violation -> Option A

4. Quick Check:

   Fail build setting missing = threshold ignored [OK]

Hint: Fail build must be enabled to enforce coverage thresholds [OK]

Common Mistakes:

• Confusing LINE and BRANCH counters
• Setting maximum instead of minimum threshold
• Believing branch coverage can't be enforced

5. You want to enforce multiple coverage thresholds in your JUnit project using JaCoCo: 85% line coverage and 75% branch coverage. Which configuration snippet correctly enforces both thresholds?

hard

A. <rules>
<rule><limit><counter>LINE</counter><value>COVEREDCOUNT</value><minimum>85</minimum></limit></rule>
<rule><limit><counter>BRANCH</counter><value>COVEREDCOUNT</value><minimum>75</minimum></limit></rule>
</rules>

B. <rules>
<rule>
<limits>
<limit><counter>LINE</counter><value>COVEREDRATIO</value><minimum>0.85</minimum></limit>
<limit><counter>BRANCH</counter><value>COVEREDRATIO</value><minimum>0.75</minimum></limit>
</limits>
</rule>
</rules>

C. <rules>
<rule><limit><counter>LINE</counter><value>MISSEDCOUNT</value><maximum>0.15</maximum></limit></rule>
<rule><limit><counter>BRANCH</counter><value>MISSEDCOUNT</value><maximum>0.25</maximum></limit></rule>
</rules>

D. <rules>
<rule><limit><counter>LINE</counter><value>COVEREDRATIO</value><minimum>0.75</minimum></limit></rule>
<rule><limit><counter>BRANCH</counter><value>COVEREDRATIO</value><minimum>0.85</minimum></limit></rule>
</rules>

Solution

1. Step 1: Check counters and values

   Use LINE and BRANCH counters with COVEREDRATIO values for coverage percentages.

2. Step 2: Verify minimum thresholds and structure

   Minimum values must be decimals (0.85 and 0.75) inside a single rule with multiple limits.

3. Final Answer:

   Rules with LINE and BRANCH counters, COVEREDRATIO values, minimum 0.85 and 0.75 -> Option B

4. Quick Check:

   Multiple limits in one rule with correct decimals [OK]

Hint: Use multiple limits inside one rule with decimals for thresholds [OK]

Common Mistakes:

• Using COVEREDCOUNT with integer minimums instead of decimals
• Swapping threshold values between LINE and BRANCH
• Splitting limits into separate rules incorrectly