Merge code coverage reports from multiple JSON ones

merge-coverage-reports.js

const fs = require('fs');
const path = require('path');
const glob = require('glob');
const istanbulReport = require('istanbul-lib-report');
const istanbulCoverage = require('istanbul-lib-coverage');
const istanbulReports = require('istanbul-reports');

const reporters = ['cobertura', 'html'];
const coverageDir = './coverage';
const coverageMergeDir = './coverage/merged';

const coverageJsonFiles = findCoverageJsonFiles(coverageDir);
const coverageMap = istanbulCoverage.createCoverageMap();
mergeCoverageJsonFilesIntoCoverageMap(coverageMap, coverageJsonFiles);
createMergedCoverageReports(coverageMap, coverageMergeDir, reporters);

function findCoverageJsonFiles(rootDir) {
  return glob
    .sync('**/coverage-final.json', { cwd: rootDir })
    .map(relativeCoverageJsonFile =>
      path.resolve(rootDir, relativeCoverageJsonFile)
    );
}

function mergeCoverageJsonFilesIntoCoverageMap(coverageMap, coverageJsonFiles) {
  coverageJsonFiles
    .map(file => JSON.parse(fs.readFileSync(file, 'utf8')))
    .forEach(coverage => coverageMap.merge(coverage));
}

function createMergedCoverageReports(coverageMap, outputDir, reporters) {
  const context = istanbulReport.createContext({ coverageMap, dir: outputDir });

  reporters.forEach(reporter => {
    istanbulReports.create(reporter, {}).execute(context);
    console.log(`${reporter} merged coverage report generated`);
  });
}