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Node.js solution for running mocha-based selenium-webdriver tests.

Getting started

Install nemo

npm install --save-dev nemo@^4

Use the scaffold feature

$ npx nemo -X test/functional


  Next steps:
  1. Make sure you have latest chrome/chromedriver installed (
     - The binary should be in your PATH
  2. Run nemo! "npx nemo"
  3. Look at nemo.config.js and test/functional/nemo.test.js
  4. Learn more:


For a more complex, fully-featured suite:

$ ./node_modules/.bin/nemo -Z test/functional

CLI arguments

$ ./bin/nemo --help

  Usage: _nemo [options]


    -V, --version                output the version number
    -B, --base-directory <path>  parent directory for config/ and spec/ (or other test file) directories. relative to cwd
    -C, --config-file <path>       config file. can be JS or JSON
    -P, --profile [profile]      which profile(s) to run, out of the configuration
    -G, --grep <pattern>         only run tests matching <pattern>
    -F, --file                   run parallel by file
    -D, --data                   run parallel by data
    -S, --server                 run the nemo web server
    -L, --logging                info level logging (errors log by default)
    -X, --scaffold <path>          inject an example nemo suite under <path>
    -Z, --scaffold-complex <path>  inject a full-featured (complex) example nemo suite under <path>
    -U, --allow-unknown-args     allow command line arguments not specified by Nemo
    -E, --exit                   force shutdown of the event loop after test run: nemo will call process.exit
    --debug-brk                  enable node's debugger breaking on the first line
    --inspect                    activate devtools in chrome
    --no-timeouts                remove timeouts in debug/inspect use case
    -h, --help                   output usage information


You may either use the confit and shortstop powered, environment-aware configuration engine, or a plain JavaScript/JSON file.

Use the "complex scaffold" feature (-Z) to create a suite with this option.


If using a plain JS/JSON file, you can add it as nemo.config.json or nemo.config.js in the directory you run nemo from. Then you can run nemo simply as ./node_modules/.bin/nemo. Nemo will find your configuration file automatically.

You can also specify a differently named or placed file using the -C option as ./node_modules/.bin/nemo -C path/to/config/config.js.

Use the "basic scaffold" feature (-X) to create a suite with this option.

Profile options


output.reports <optional>

This convenience setting will create timestamped and tag-based directory structure for reports and screenshots when you use mochawesome or xunit reporters. When you use this, you can omit the specific directory/filename settings for those reporters, as nemo will take care of that for you.

Recommended to set this as path:report, which will create a report directory beneath your base directory. See Reporting below. <optional>

You can provide an influxdb endpoint and store test results in it. E.g.

"storage": {
    "server": "localhost",
    "database": "nemo"


Currently, you will get two measurements from running tests, test and lifecycle:

schema: [{
  measurement: 'test',
  fields: {
    result: Influx.FieldType.STRING,
    error: Influx.FieldType.STRING,
    stack: Influx.FieldType.STRING,
    fullTitle: Influx.FieldType.STRING,
    duration: Influx.FieldType.INTEGER,
    threadID: Influx.FieldType.STRING,
    masterID: Influx.FieldType.STRING
  tags: [
  measurement: 'lifecycle',
  fields: {
    event: Influx.FieldType.STRING,
    threadID: Influx.FieldType.STRING,
    masterID: Influx.FieldType.STRING,
    duration: Influx.FieldType.INTEGER
  tags: [

output.listeners <optional>

The output:listeners property can resolve to a function, an Object, or an Array (or Array of Arrays) of functions/objects.

The function form:

module.exports = function (emitter) {
  emitter.on('test', (context, event) => {
    console.log(`another testlistener ${event.test.title} status: ${event.test.state}`);

The Object form:

  type: 'pass',
  listener: (context, event) => {
    console.log(`user event listener: test passed ${JSON.stringify(event.tags)}`);

Please see "Events" section for more details


is the main profile configuration that others will merge into


is an absolute path based glob pattern. (e.g. "tests": "path:spec/!(wdb)*.js",)


only valid for 'base'.

  • if set to 'file' it will create a child process for each mocha file (alternative to -F CLI arg)
  • if set to 'data' it will create a child process for each object key under (alternative to the -D CLI arg)


mocha options. described elsewhere


any environment variables you want in the test process.


-if set to true, nemo will always exit with zero code -if set to false, or don't set any value, the exitCode is Math.min(, 255);


  • currently base.env is only honored if nemo is launching parallel nemo instances (each as its own process). If nemo launches a single nemo instance in the main process, these are ignored.
  • any env variables in your nemo process will be merged into the env for the parallel processes (along with whatever is set under base.env)


a number which represents the max limit of concurrent suites nemo will execute in parallel - if not provided there is no limit


If you use either of the built-in reporters (xunit or mochawesome), nemo will generate timestamped directories for each run. The reports will be further separated based on the parallel options. E.g.


In the above example, parallel options were "profile", "file", and "data".

A summary for all parallel instances can be found at summary.json


You can use nemo.snap() at any point in a test, to grab a screenshot. These screenshots will be named based on the respective test name, and number of screenshots taken using nemo.snap(). E.g.

  • my awesome test.1.png
  • my awesome test.2.png
  • my awesome test.3.png

If you use the mochawesome reporter, you will see these screeshots in the Additional Context section of the html report.

If you are using mochawesome or xunit along with the output.reports setting, screenshots will be placed in the appropriate output directory based on the instance details of the test which generated them.

Adding Nemo into the mocha context and vice versa

nemo injects a nemo instance into the Mocha context (for it, before, after, etc functions) which can be accessed by this.nemo within the test suites.

nemo also adds the current test's context to nemo.mocha. That can be useful if you want to access or modify the test's context from within a nemo plugin.

Parallel functionality

nemo will execute in parallel -P (profile) x -G (grep) mocha instances. The example above uses "browser" as the profile dimension and suite name as the "grep" dimension. Giving 2x2=4 parallel executions.

In addition to profile and grep, are the dimensions file and data.

Parallel by file

file will multiply the existing # of instances by the # of files selected by your configuration.

Parallel by data

data will multiply the existing # of instances by the # of keys found under It can also be overriden per-profile. It will also replace with the value of each keyed object. In other words, you can use this to do parallel, data-driven testing.

If you have the following base profile configuration:

  "profiles": {
    "base": {
      "data": {
        "US": {"url": ""},
        "FR": {"url": ""}
      "parallel": "data",
      "tests": "path:spec/test-spec.js",
      "mocha": {

Then the following test will run twice (in parallel) with corresponding values of

it('@loadHome@', function () {
    var nemo = this.nemo;
    return nemo.driver.get(;//runs once with, once with

Parallel reporting

Using a reporter which gives file output will be the most beneficial. nemo comes out of the box, ready to use mochawesome or xunit for outputting a report per parallel instance.

Mocha options

The properties passed in to the "mocha" property of config.json will be applied to the mocha instances that are created. In general, these properties correlate with the mocha command line arguments. E.g. if you want this:

mocha --timeout 180000

You should add this to the "mocha" property within "profiles" of config.json:

"profile": {
	...other stuff,
	"mocha": {
		"timeout": 180000

nemo creates mocha instances programmatically. Unfortunately, not all mocha command line options are available when instantiating it this way. One of the arguments that is not supported is the --require flag, which useful if you want to require a module, e.g. babel-register (for Babel v6) or @babel/register (for Babel v7) for transpilation. Thus, we added a "require" property in nemo.config.json profile/base/mocha block, which takes a string of a single npm module name, or an array of npm module names. If it is an array, nemo will require each one before instantiating the mocha instances.


Nemo publishes lifecycle events which can help to monitor progress.


Published when an instance starts. The event is an object.

Property Type Description
tags Tags{object}


Published when an instance ends. The event is an InstanceResult object.


This event is published when all instances are completed. The event is an array of InstanceResult objects.


This event is published when root suite execution started


This event is published when suite execution started


This event is published when suite finish


This event is published when test execution started. The event is an object. You can use "uid" to correlate this event with other test events from the same instance.

Property Type Description
tags Tags{object}
test TestResult modified Mocha test object, not with all values as test event (see elsewhere)


This event is published at the conclusion of a test. The event is an object. You can use "uid" to correlate this event with other test events from the same instance.

Property Type Description
tags Tags{object}
test TestResult modified Mocha test object (see elsewhere)
duration ms{number} Run duration for this test

<custom events>

You can publish custom events from within your tests using nemo.runner.emit(EventType{string}[, EventPayload{object}])

Nemo will publish this on the main event listener as the following object

Property Type Description
tags Tags{object}
payload EventPayload{object} user defined, or empty object

Common event objects


Property Type Description
tags Tags{object}
testResults TestResult[]
duration ms{number} Run duration for this instance


Modified Mocha test object

Property Type Description
file {string} path to file containing this test
fullTitleString {string} Suite and test title concatenated
state {string} passed or failed
duration ms{number} Run duration for this test

Many other properties. Inspect in debugger for more information


Property Type Description
profile {string} The profile which spawned this instance
uid {string} unique identifier for this instance
reportFile (optional) {string} path to report file for this instance (if generated)
grep (optional) {string} grep string, if provided
data (optional) {string} data key for this instance, if parallel by data is being used

Webdriver lifecycle options


Leave this unset, or set to false for a webdriver per Suite. Set to true for a webdriver per test

Example (find this in the test configuration):

"driverPerSuite": {
    "tests": "path:./lifecycle.js",
    "driverPerTest": false,
    "mocha": {
        "grep": "@entireSuite@"
"driverPerTest": {
    "tests": "path:./lifecycle.js",
    "driverPerTest": true,
    "mocha": {
        "grep": "@eachTest@"

When driverPerSuite is true the global beforeEach hook will have a nemo instance injected, but not when driverPerSuite is false

Please note: When using the driverPerTest option, there will be no reliable nemo instance in the before/after lifecycle context.

Custom CLI Options (feature incomplete)

By default, Nemo will not accept CLI arguments that are not listed under CLI Arguments

Custom arguments can be useful for programmatically customizing Nemo configuration.

Use -U or --allow-unknown-args to prevent Nemo from validating CLI arguments

$ ./bin/nemo -U --myCustomArg myValue --anotherArg

Further enhancement must be made in order to take advantage of custom arguments when running in parallel mode. Please see #21


node.js selenium-webdriver/mocha based combined testing framework






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