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Primitive load-balancer to run Cypress specs in parallel on CI without recording
/**
* Primitive load-balancer to split Cypress specs across multiple runners. This script assumes that
* all your specs are in the folder '<project root>/cypress/integration'. It uses the number of
* tests per spec file as sole criteria to split specs between runners.
*
* This script accepts two arguments: the total number of runners and the index (starting from 0) of
* the current runner. Example:
* $ node cypress-partial.js 5 2
* This command asks for specs to give to the third runner of five runners.
* The output of the script is a coma-separated list of specs that can be given to Cypress. Example:
* cypress/integration/some.spec.ts,cypress/integration/another.spec.ts
*
* Lets assume you have five runners (virtual machines) to run specs in parallel on your CI, and
* each runner knows its number (from 0 to 4). So the third runner must execute its spec as
* following:
* $ cypress run --spec $(node cypress-partial.js 5 2)
*
* Here as example for GitHub actions:
*
* jobs:
* e2e:
* runs-on: ubuntu-latest
* strategy:
* fail-fast: false
* matrix:
* containers: [ 0, 1, 2, 3, 4 ]
* steps:
* - name: E2E
* run: cypress run --spec $(node cypress-partial.js 5 ${{ matrix.containers }})
*/
const fs = require('fs/promises');
const specDir = 'cypress/integration';
const testPattern = /(^|\s)(it|test)\(/g;
const [ totalRunners, thisRunner ] = process.argv.splice(2);
fs.readdir(specDir).then(async files => {
const nbTests = {};
for (const file of files) {
nbTests[file] = await testCount(file);
}
const chunks = [];
Object
.entries(nbTests)
.sort((a, b) => b[1] - a[1])
.map(entry => entry[0])
.map(file => `${specDir}/${file}`)
.forEach((file, index) => {
const chunk = index % totalRunners;
chunks[chunk] ||= [];
chunks[chunk].push(file);
});
const output = chunks[thisRunner].join(',');
return console.log(output);
});
async function testCount(filename) {
const content = await fs.readFile(`${specDir}/${filename}`, 'utf8');
return content.match(testPattern).length;
}
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