jacoco

name	jacoco
description	Check JaCoCo code coverage for a Maven/Java project against a coverage gate, then drill into per-module, per-class, and per-line gaps to target tests. Use when checking coverage, finding uncovered code, or planning tests to reach a coverage threshold.
argument-hint	[module-or-class]

Check JaCoCo Code Coverage

Try it: /maven-quality:jacoco payment-service — or say "what's our test coverage on the payment service?".

Run verify to generate coverage reports, then parse and display the results. Defaults target a Maven/Java project with the JaCoCo plugin bound so that verify produces target/site/jacoco/jacoco.xml.

Coverage gate: 80% line coverage (default)

Adjust THRESHOLD in the snippets below to match your project's gate.

Adjusting for your project

• Maven invocation: examples use the wrapper ./mvnw. If your environment has no wrapper, substitute your mvn binary, e.g. bash "/path/to/mvn" verify -f pom.xml -q.
• Single module / non-modular project: the report lives at target/site/jacoco/jacoco.xml. Set modules = ['.'] and use '.'/target/... paths, or just drop the module prefix.
• Multi-module project: set the modules list to your module directory names, or pass one module as the argument to scope to it.
• $ARGUMENTS (when present) is treated as either a module name (Steps 1, 2, 5, 7) or a class source-file name (Step 4).

Step 1: Generate coverage reports

Specific module (e.g. argument = my-core):

./mvnw verify -pl $ARGUMENTS -q

All modules / whole project:

./mvnw clean verify -q

Step 2: Module-level summary (PASS/FAIL vs gate)

python3 -c "
import xml.etree.ElementTree as ET

THRESHOLD = 80
# Adjust to your module directory names, or use ['.'] for a single-module project.
modules = ['module-a', 'module-b', 'module-c']
if '$ARGUMENTS':
    modules = ['$ARGUMENTS']

print(f'{\"Module\":<24} {\"Covered\":>8} {\"Total\":>8} {\"Coverage\":>10} {\"Status\":>8}')
print('-' * 62)
for module in modules:
    path = f'{module}/target/site/jacoco/jacoco.xml' if module != '.' else 'target/site/jacoco/jacoco.xml'
    try:
        root = ET.parse(path).getroot()
        for counter in root.findall('counter'):
            if counter.get('type') == 'LINE':
                missed = int(counter.get('missed'))
                covered = int(counter.get('covered'))
                total = missed + covered
                pct = covered / total * 100 if total > 0 else 0
                status = 'PASS' if pct >= THRESHOLD else 'FAIL'
                print(f'{module:<24} {covered:>8} {total:>8} {pct:>9.2f}% {status:>8}')
    except FileNotFoundError:
        print(f'{module:<24} {\"N/A\":>8} {\"N/A\":>8} {\"N/A\":>10} {\"MISSING\":>8}')
"

Step 3: Class-level breakdown (lowest coverage first)

python3 -c "
import xml.etree.ElementTree as ET

module = '$ARGUMENTS' if '$ARGUMENTS' else 'module-a'
path = f'{module}/target/site/jacoco/jacoco.xml' if module != '.' else 'target/site/jacoco/jacoco.xml'
root = ET.parse(path).getroot()
results = []
for pkg in root.findall('.//package'):
    for cls in pkg.findall('class'):
        for counter in cls.findall('counter'):
            if counter.get('type') == 'LINE':
                missed = int(counter.get('missed'))
                covered = int(counter.get('covered'))
                total = missed + covered
                if total > 0:
                    results.append((covered / total * 100, missed, covered, total, cls.get('name')))
results.sort()
print(f'{\"Coverage\":>10} {\"Missed\":>8} {\"Covered\":>8} {\"Total\":>8}  Class')
print('-' * 80)
for pct, missed, covered, total, name in results:
    print(f'{pct:>9.1f}% {missed:>8} {covered:>8} {total:>8}  {name}')
"

Step 4: Uncovered lines in a specific class

Set CLASS_NAME (or pass the class source file as the argument) to find exact uncovered line numbers for targeted test writing:

python3 -c "
import xml.etree.ElementTree as ET

module = 'module-a'  # adjust to the module containing the class, or '.'
path = f'{module}/target/site/jacoco/jacoco.xml' if module != '.' else 'target/site/jacoco/jacoco.xml'
root = ET.parse(path).getroot()

CLASS_NAME = '$ARGUMENTS.java' if '$ARGUMENTS' else 'REPLACE_ME.java'

for pkg in root.findall('.//package'):
    for sf in pkg.findall('sourcefile'):
        if sf.get('name') == CLASS_NAME:
            uncovered = [int(line.get('nr')) for line in sf.findall('line') if int(line.get('mi', 0)) > 0]
            print(f'Uncovered lines in {CLASS_NAME}: {len(uncovered)} lines')
            for ln in uncovered:
                print(f'  Line {ln}')
"

Step 5: Gap analysis (lines needed to reach the gate)

python3 -c "
import xml.etree.ElementTree as ET
import math

THRESHOLD = 80
modules = ['module-a', 'module-b', 'module-c']
if '$ARGUMENTS':
    modules = ['$ARGUMENTS']

for module in modules:
    path = f'{module}/target/site/jacoco/jacoco.xml' if module != '.' else 'target/site/jacoco/jacoco.xml'
    try:
        root = ET.parse(path).getroot()
        for counter in root.findall('counter'):
            if counter.get('type') == 'LINE':
                missed = int(counter.get('missed'))
                covered = int(counter.get('covered'))
                total = missed + covered
                pct = covered / total * 100 if total > 0 else 0
                needed = math.ceil(THRESHOLD / 100 * total) - covered
                if needed > 0:
                    print(f'{module}: {pct:.2f}% — need {needed} more lines covered to reach {THRESHOLD}%')
                else:
                    print(f'{module}: {pct:.2f}% — ALREADY above {THRESHOLD}% (surplus: {-needed} lines)')
    except FileNotFoundError:
        print(f'{module}: No coverage report found')
"

Step 6: Quick-win targets (classes with the smallest gaps)

python3 -c "
import xml.etree.ElementTree as ET

module = '$ARGUMENTS' if '$ARGUMENTS' else 'module-a'
path = f'{module}/target/site/jacoco/jacoco.xml' if module != '.' else 'target/site/jacoco/jacoco.xml'
root = ET.parse(path).getroot()
results = []
for pkg in root.findall('.//package'):
    for cls in pkg.findall('class'):
        for counter in cls.findall('counter'):
            if counter.get('type') == 'LINE':
                missed = int(counter.get('missed'))
                covered = int(counter.get('covered'))
                total = missed + covered
                if total > 0 and missed > 0:
                    results.append((missed, covered, total, cls.get('name')))

results.sort(key=lambda x: x[0])  # fewest missed lines first
print(f'{\"Missed\":>8} {\"Covered\":>8} {\"Total\":>8} {\"Coverage\":>10}  Class')
print('-' * 80)
for missed, covered, total, name in results[:20]:
    print(f'{missed:>8} {covered:>8} {total:>8} {covered / total * 100:>9.1f}%  {name}')
"

Step 7: Full summary (LINE, BRANCH, METHOD, CLASS)

python3 -c "
import xml.etree.ElementTree as ET

modules = ['module-a', 'module-b', 'module-c']
if '$ARGUMENTS':
    modules = ['$ARGUMENTS']

for module in modules:
    path = f'{module}/target/site/jacoco/jacoco.xml' if module != '.' else 'target/site/jacoco/jacoco.xml'
    try:
        root = ET.parse(path).getroot()
        print(f'\n=== {module} ===')
        print(f'{\"Type\":<12} {\"Covered\":>8} {\"Missed\":>8} {\"Total\":>8} {\"Coverage\":>10}')
        print('-' * 50)
        for counter in root.findall('counter'):
            ctype = counter.get('type')
            missed = int(counter.get('missed'))
            covered = int(counter.get('covered'))
            total = missed + covered
            pct = covered / total * 100 if total > 0 else 0
            print(f'{ctype:<12} {covered:>8} {missed:>8} {total:>8} {pct:>9.2f}%')
    except FileNotFoundError:
        print(f'\n=== {module} === NO REPORT FOUND')
"

Coverage improvement strategy

When coverage is below the gate:

1. Run gap analysis (Step 5) to see how many lines are needed.
2. Run quick-win targets (Step 6) to find classes with the fewest missed lines.
3. Run uncovered lines (Step 4) on those classes to find exact lines.
4. Write tests targeting those lines:
   • Use @ParameterizedTest to efficiently cover multiple code paths.
   • Use Mockito for external dependencies.
   • Focus on error/exception paths, which are often uncovered.
5. Re-run verify and the summary to confirm improvement.