Coverage thresholds in JUnit - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the minimum line coverage threshold to 80%.

JUnit

@Rule
public final TestRule coverage = new CoverageRule().withLineThreshold([1]);

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

A75

B90

C80

D70

Attempts:

3 left

💡 Hint

Common Mistakes

Using a value less than desired threshold like 70 instead of 80.

Including the % sign in the number.

The method withLineThreshold sets the minimum line coverage percentage. Here, 80 means 80% coverage is required.

2fill in blank

medium

Complete the code to fail the test if branch coverage is below 85%.

JUnit

@Rule
public final TestRule coverage = new CoverageRule().withBranchThreshold([1]);

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

A80

B85

C90

D75

Attempts:

3 left

💡 Hint

Common Mistakes

Setting the threshold too low, which may allow insufficient coverage.

Confusing line coverage with branch coverage.

The withBranchThreshold method sets the minimum branch coverage percentage. 85 means the test fails if branch coverage is below 85%.

3fill in blank

hard

Fix the error in the code to correctly set the coverage threshold to 75%.

JUnit

@Rule
public final TestRule coverage = new CoverageRule().withLineThreshold([1]);

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

A75

B"75%"

C0.75

DseventyFive

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string with % sign like "75%".

Using a decimal like 0.75 instead of 75.

The threshold value must be an integer representing the percentage without quotes or decimals. So 75 is correct.

4fill in blank

hard

Fill both blanks to set line coverage to 80% and branch coverage to 70%.

JUnit

@Rule
public final TestRule coverage = new CoverageRule()
    .withLineThreshold([1])
    .withBranchThreshold([2]);

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

A80

B70

C75

D85

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the values between line and branch thresholds.

Using values outside typical coverage ranges.

The first blank sets line coverage threshold to 80%, the second sets branch coverage threshold to 70%.

5fill in blank

hard

Fill all three blanks to set line coverage to 85%, branch coverage to 80%, and fail on uncovered methods.

JUnit

@Rule
public final TestRule coverage = new CoverageRule()
    .withLineThreshold([1])
    .withBranchThreshold([2])
    .failOnUncoveredMethods([3]);

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

Atrue

Bfalse

C80

D85

Attempts:

3 left

💡 Hint

Common Mistakes

Using false instead of true for failOnUncoveredMethods.

Mixing up the coverage threshold values.

Set line coverage to 85 (D), branch coverage to 80 (C), and enable fail on uncovered methods with true (A).

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