lean-coverage-listener

Leightweight agent

Light agent for coverage collection using Node V8 Coverage

Configuration

Cli argument can’t be used directly with a lightweight agent. It should be passed via file sl.conf file or via env var. Env var should be prefixed by SL_

Default values

Name	Default value
tokenFile	sltoken.txt
buildSessionIdFile	buildSessionId
projectRoot	process.cwd();

Usage

Preloader script should be injected/installed beforehand. For example, into ./agent/lightweight.js

Define execution of lightweight agent before main script by setting env var NODE_OPTIONS="-r <path to agent>" for instance NODE_OPTIONS="-r ./node_modules/lean-coverage-collector/preloader.js"

When you need define folder where coverage footprints will be stored. You can provide NODE_V8_COVERAGE env. Otherwise, default folder .sl-cov will be used.

By default, coverage listener will be executed in a child process but it can be configured

Run in the same process

Env var SL_IN_PROCESS_COVERAGE_COLLECTION can be passed to run coverage listener in a same process with tested app. Also if you want everything to be executed in one process you also need to pass NODE_V8_COVERAGE explicitly. Otherwise, app will be executed in a separate process.

It will cause sending of extra hits because internal hits from agent will be sent. But it won't have impact on coverage accuracy.

Run in sidecar

Run in a sidecar allow to collect coverage from other processes via file system (even more from one at once). To do that agent should be started directly like npx lean-coverage-collector. For correct work it require env NODE_V8_COVERAGE to be defined. Also all processes that will provide coverage should call method v8.takeCoverage() periodically.

To achive that, process can be executed with preloader and option SL_SKIP_PRELOADER=1. In that case preloader main logic won't be executed but will be defined a timer to take coverage each 10 sec. It will prevent execution of preloader script and will set a timer for coverage snapshots generation.

WARN: Usage of preloader without SL_SKIP_PRELOADER=1 parameter will create new instance of agent that will conflict with a sidecar instance

Also separate script ./node_modules/lean-coverage-collector/coverage-collector.js can be used. Just run it before execution via -r option

Another option is to modify the itself and add import of coverage-collector.js or just add next code:

cosnt v8 = require('v8');

const timer = setInterval(() => {
    log('Get coverage');
    v8.takeCoverage();
}, +process.env['SL_COVERAGE_INTERVAL']);
timer.unref();

Example: Run of agent in a sidecar

export NODE_V8_COVERAGE=.sl-cov
npx lean-coverage-collector
OR
node ./node_modules/lean-coverage-collector/runner.js

Run of observable process

export NODE_V8_COVERAGE=.sl-cov
export SL_SKIP_PRELOADER=1
node -r ./node_modules/lean-coverage-collector/preloader.js ./dist/server.js

or

export NODE_V8_COVERAGE=.sl-cov
node -r ./node_modules/lean-coverage-collector/coverage-collector.js ./dist/server.js