Do I need to run selenium server when using chromedriver?

Question

I'm new to Selenium and Nightwatch and installed selenium-webdriver first, then chromedriver and finally I installed Nightwatch (because the syntax looks nice to me). Now when I want to run a single test with nightwatch, I always get this result:

> ./node_modules/nightwatch/bin/nightwatch -t nightwatch-node-scripts/test.js 
[Test] Test Suite
=====================
Running: Demo test Google
Error processing the server response: 
 unknown command: wd/hub/session
Error retrieving a new session from the selenium server
Connection refused! Is selenium server started?
{ value: -1, error: 'Unexpected token u in JSON at position 0' }

The chromedriver is running and listening on port 9515:

> lsof -Pnl +M -i4 | grep 9515
chromedri 6489 1000 8u IPv4 867952 0t0 TCP 127.0.0.1:9515 (LISTEN)

which is the one I use in my pretty basic nightwatch.json:

{
 "src_folders": ["tests"],
 "output_folder": "reports",
 "custom_commands_path": "",
 "custom_assertions_path": "",
 "page_objects_path": "",
 "globals_path": "",
 "selenium": {
 "start_process": false,
 "server_path": "",
 "log_path": "",
 "port": 4444,
 "cli_args": {
 "webdriver.chrome.driver": "/usr/local/bin/chromedriver",
 "webdriver.gecko.driver": "",
 "webdriver.edge.driver": ""
 }
 },
 "test_settings": {
 "default": {
 "launch_url": "http://localhost",
 "selenium_port": 9515,
 "selenium_host": "localhost",
 "silent": true,
 "screenshots": {
 "enabled": false,
 "path": ""
 },
 "desiredCapabilities": {
 "browserName": "chrome",
 "chromeOptions" : {
 "args" : ["--no-sandbox"]
 },
 "acceptsCerts" : true
 }
 },
 "chrome": {
 "desiredCapabilities": {
 "browserName": "chrome"
 }
 },
 }
}

• Kate Paulk: With that error message, I'm inclined to say that you need to have an active Selenium session to run your test.
• RSeidelsohn: OK, thank you. My first understanding told me that chrome driver would replace the selenium server, which is why I was confused.
• kirbycope: Selenium Standalone Server can be used to define a 'hub' and 'nodes'. The hub distributes tests and the nodes run them (using WebDriver).
• Shailendra Rathore: stackoverflow.com/questions/27225118/… hope it help you @RSeidelsohn

Answer 1

From Selenium Documentation:

You may, or may not, need the Selenium Server, depending on how you intend to use Selenium-WebDriver. If your browser and tests will all run on the same machine, and your tests only use the WebDriver API, then you do not need to run the Selenium-Server; WebDriver will run the browser directly.

There are some reasons though to use the Selenium-Server with Selenium-WebDriver.

You are using Selenium-Grid to distribute your tests over multiple machines or virtual machines (VMs). You want to connect to a remote machine that has a particular browser version that is not on your current machine. You are not using the Java bindings (i.e. Python, C#, or Ruby) and would like to use HtmlUnit Driver

• x-yuri: Which brings up a question if Nightwatch can use Webdriver API. Judging from it having server_path and start_process options, it can't. Or am I wrong? Come to think of it which tools do you know that can? Does starting Selenium Server means Webdriver protocol (or what's its name) can't be used?