merge-reports.ts

const glob = require('glob');
const fs = require('fs');
const path = require('path');

const getLcovFiles = function (src) {
  return new Promise((resolve, reject) => {
    glob(`${src}/**/lcov.info`, (error, result) => {
      if (error) return reject(error);
      resolve(result);
    });
  })
};

(async function(){
  const files:any  = await getLcovFiles('coverage');
  // if no files reset directory
  // if (files.length === 0) {
  //   // remove directory
  //   fs.rmdirSync('coverage', { recursive: true });
  //   fs.mkdirSync('coverage');
  // }
  // const cypressFiles = await getLcovFiles('apps/**/coverage')
  
  // files = [...files, ...cypressFiles];
  const mergedReport = files.reduce((mergedReport, currFile) => mergedReport += fs.readFileSync(currFile), '');
  const mergedFile = path.resolve('./coverage/lcov.info');
  
  // remove old merged file
  if (fs.existsSync(mergedFile)) {
    fs.unlinkSync(mergedFile);
  }

  await fs.writeFile(mergedFile, mergedReport, (err) => {
    if (err) throw err;
    console.log('The file has been saved!');
  });
})();