Step 1: Generate Coverage Report

JavaScript/TypeScript (Jest):

npm test -- --coverage --coverageReporters=text --coverageReporters=lcov

JavaScript/TypeScript (Vitest):

vitest run --coverage

Python (pytest):

pytest --cov=src --cov-report=html --cov-report=term-missing

Go:

go test -coverprofile=coverage.out ./...
go tool cover -html=coverage.out

Step 2: Analyze Coverage Metrics

Review these key metrics:

Line coverage: Percentage of lines executed
Branch coverage: Percentage of conditional branches tested
Function coverage: Percentage of functions called
Statement coverage: Percentage of statements executed

Target thresholds:

Critical code: 80%+ coverage
Standard code: 60%+ coverage
UI/Config: 40%+ coverage

Step 3: Identify Gaps

Look for:

Uncovered functions: Functions with 0% coverage
Partial coverage: Functions with <50% coverage
Missing branches: Untested if/else paths
Error paths: Untested catch blocks
Edge cases: Boundary conditions not tested

Step 4: Prioritize Testing

High Priority (test first):

Business logic with 0% coverage
Security-critical functions
Payment/transaction code
Data validation logic
Error handling paths

Medium Priority (test next):

API endpoints
Database operations
Utility functions
Configuration logic

Low Priority (test if time permits):

Simple getters/setters
UI presentation logic
Type definitions
Generated code

Step 5: Create Action Plan

For each gap:

Identify the untested code
Determine test type needed (unit/integration/e2e)
Estimate effort (small/medium/large)
Assign priority (high/medium/low)
Create test implementation tasks

Common Patterns

Pattern: Find untested files

# Jest
npm test -- --coverage --collectCoverageFrom='src/**/*.{js,ts}' --coverageThreshold='{"global":{"lines":0}}'

# pytest
pytest --cov=src --cov-report=term-missing | grep "0%"

Pattern: Check specific module

# Jest
npm test -- path/to/module --coverage

# pytest
pytest tests/test_module.py --cov=src.module --cov-report=term-missing

Pattern: Enforce coverage thresholds

// package.json (Jest)
{
  "jest": {
    "coverageThreshold": {
      "global": {
        "branches": 70,
        "functions": 70,
        "lines": 70,
        "statements": 70
      }
    }
  }
}

Advanced

For detailed information, see:

Coverage Tools - Tool-specific configuration and usage
Testing Patterns - Common testing patterns and best practices

test-coverage-analyzer

Test Coverage Analyzer

Quick Start

Instructions