これは、このセクションの複数ページの印刷可能なビューです。 印刷するには、ここをクリックしてください.

このページの通常のビューに戻る.

Troubleshooting Assistance

How to get manage WebDriver problems.

It is not always obvious the root cause of errors in Selenium.

  1. The most common Selenium-related error is a result of poor synchronization. Read about Waiting Strategies. If you aren’t sure if it is a synchronization strategy you can try temporarily hard coding a large sleep where you see the issue, and you’ll know if adding an explicit wait can help.

  2. Note that many errors that get reported to the project are actually caused by issues in the underlying drivers that Selenium sends the commands to. You can rule out a driver problem by executing the command in multiple browsers.

  3. If you have questions about how to do things, check out the Support options for ways get assistance.

  4. If you think you’ve found a problem with Selenium code, go ahead and file a Bug Report on GitHub.

1 - Understanding Common Errors

How to get deal with various problems in your Selenium code.

Invalid Selector Exception

CSS and XPath Selectors are sometimes difficult to get correct.

Likely Cause

The CSS or XPath selector you are trying to use has invalid characters or an invalid query.

Possible Solutions

Run your selector through a validator service:

Or use a browser extension to get a known good value:

No Such Element Exception

The element can not be found at the exact moment you attempted to locate it.

Likely Cause

  • You are looking for the element in the wrong place (perhaps a previous action was unsuccessful).
  • You are looking for the element at the wrong time (the element has not shown up in the DOM, yet)
  • The locator has changed since you wrote the code

Possible Solutions

  • Make sure you are on the page you expect to be on, and that previous actions in your code completed correctly
  • Make sure you are using a proper Waiting Strategy
  • Update the locator with the browser’s devtools console or use a browser extension like:

Stale Element Reference Exception

An element goes stale when it was previously located, but can not be currently accessed. Elements do not get relocated automatically; the driver creates a reference ID for the element and has a particular place it expects to find it in the DOM. If it can not find the element in the current DOM, any action using that element will result in this exception.

Common Causes

This can happen when:

  • You have refreshed the page, or the DOM of the page has dynamically changed.
  • You have navigated to a different page.
  • You have switched to another window or into or out of a frame or iframe.

Common Solutions

The DOM has changed

When the page is refreshed or items on the page have moved around, there is still an element with the desired locator on the page, it is just no longer accessible by the element object being used, and the element must be relocated before it can be used again. This is often done in one of two ways:

  • Always relocate the element every time you go to use it. The likelihood of the element going stale in the microseconds between locating and using the element is small, though possible. The downside is that this is not the most efficient approach, especially when running on a remote grid.

  • Wrap the Web Element with another object that stores the locator, and caches the located Selenium element. When taking actions with this wrapped object, you can attempt to use the cached object if previously located, and if it is stale, exception can be caught, the element relocated with the stored locator, and the method re-tried. This is more efficient, but it can cause problems if the locator you’re using references a different element (and not the one you want) after the page has changed.

The Context has changed

Element objects are stored for a given context, so if you move to a different context — like a different window or a different frame or iframe — the element reference will still be valid, but will be temporarily inaccessible. In this scenario, it won’t help to relocate the element, because it doesn’t exist in the current context. To fix this, you need to make sure to switch back to the correct context before using the element.

The Page has changed

This scenario is when you haven’t just changed contexts, you have navigated to another page and have destroyed the context in which the element was located. You can’t just relocate it from the current context, and you can’t switch back to an active context where it is valid. If this is the reason for your error, you must both navigate back to the correct location and relocate it.

2 - Logging Selenium commands

Getting information about Selenium execution.

Turning on logging is a valuable way to get extra information that might help you determine why you might be having a problem.

Getting a logger

Java logs are typically created per class. You can work with the default logger to work with all loggers. To filter out specific classes, see Filtering

Get the root logger:

    Logger logger = Logger.getLogger("");
Check code on GitHub

Java Logging is not exactly straightforward, and if you are just looking for an easy way to look at the important Selenium logs, take a look at the Selenium Logger project

Python logs are typically created per module. You can match all submodules by referencing the top level module. So to work with all loggers in selenium module, you can do this:

    logger = logging.getLogger('selenium')
Check code on GitHub 
.NET does not currently have a Logging implementation

If you want to see as much debugging as possible in all the classes, you can turn on debugging globally in Ruby by setting $DEBUG = true.

For more fine-tuned control, Ruby Selenium created its own Logger class to wrap the default Logger class. This implementation provides some interesting additional features. Obtain the logger directly from the #loggerclass method on the Selenium::WebDriver module:

      logger = Selenium::WebDriver.logger
Check code on GitHub 
const logging = require('selenium-webdriver/lib/logging')
logger = logging.getLogger('webdriver')

Logger level

Logger level helps to filter out logs based on their severity.

Java has 7 logger levels: SEVERE, WARNING, INFO, CONFIG, FINE, FINER, and FINEST. The default is INFO.

You have to change both the level of the logger and the level of the handlers on the root logger:

    logger.setLevel(Level.FINE);
    Arrays.stream(logger.getHandlers()).forEach(handler -> {
      handler.setLevel(Level.FINE);
    });
Check code on GitHub

Python has 6 logger levels: CRITICAL, ERROR, WARNING, INFO, DEBUG, and NOTSET. The default is WARNING

To change the level of the logger:

    logger.setLevel(logging.DEBUG)
Check code on GitHub

Things get complicated when you use PyTest, though. By default, PyTest hides logging unless the test fails. You need to set 3 things to get PyTest to display logs on passing tests.

To always output logs with PyTest you need to run with additional arguments. First, -s to prevent PyTest from capturing the console. Second, -p no:logging, which allows you to override the default PyTest logging settings so logs can be displayed regardless of errors.

So you need to set these flags in your IDE, or run PyTest on command line like:

pytest -s -p no:logging

Finally, since you turned off logging in the arguments above, you now need to add configuration to turn it back on:

logging.basicConfig(level=logging.WARN)

.NET does not currently have a Logging implementation

Ruby logger has 5 logger levels: :debug, :info, :warn, :error, :fatal. As of Selenium v4.9.1, The default is :info.

To change the level of the logger:

      logger.level = :debug
Check code on GitHub

JavaScript has 9 logger levels: OFF, SEVERE, WARNING, INFO, DEBUG, FINE, FINER, FINEST, ALL. The default is OFF.

To change the level of the logger:

logger.setLevel(logging.Level.INFO)

Actionable items

Things are logged as warnings if they are something the user needs to take action on. This is often used for deprecations. For various reasons, Selenium project does not follow standard Semantic Versioning practices. Our policy is to mark things as deprecated for 3 releases and then remove them, so deprecations may be logged as warnings.

Java logs actionable content at logger level WARN

Example:

May 08, 2023 9:23:38 PM dev.selenium.troubleshooting.LoggingTest logging
WARNING: this is a warning

Python logs actionable content at logger level — WARNING Details about deprecations are logged at this level.

Example:

WARNING  selenium:test_logging.py:23 this is a warning

.NET does not currently have a Logging implementation

Ruby logs actionable content at logger level — :warn. Details about deprecations are logged at this level.

For example:

2023-05-08 20:53:13 WARN Selenium [:example_id] this is a warning

Because these items can get annoying, we’ve provided an easy way to turn them off, see filtering section below.

Useful information

This is the default level where Selenium logs things that users should be aware of but do not need to take actions on. This might reference a new method or direct users to more information about something

Java logs useful information at logger level INFO

Example:

May 08, 2023 9:23:38 PM dev.selenium.troubleshooting.LoggingTest logging
INFO: this is useful information

Python logs useful information at logger level — INFO

Example:

INFO     selenium:test_logging.py:22 this is useful information

.NET does not currently have a Logging implementation

Ruby logs useful information at logger level — :info.

Example:

2023-05-08 20:53:13 INFO Selenium [:example_id] this is useful information

Logs useful information at level: INFO

Debugging Details

The debug log level is used for information that may be needed for diagnosing issues and troubleshooting problems.

Java logs most debug content at logger level FINE

Example:

May 08, 2023 9:23:38 PM dev.selenium.troubleshooting.LoggingTest logging
FINE: this is detailed debug information

Python logs debugging details at logger level — DEBUG

Example:

DEBUG    selenium:test_logging.py:24 this is detailed debug information

.NET does not currently have a Logging implementation

Ruby only provides one level for debugging, so all details are at logger level — :debug.

Example:

2023-05-08 20:53:13 DEBUG Selenium [:example_id] this is detailed debug information

Logs debugging details at level: FINER and FINEST

Logger output

Logs can be displayed in the console or stored in a file. Different languages have different defaults.

By default all logs are sent to System.err. To direct output to a file, you need to add a handler:

    Handler handler = new FileHandler("selenium.xml");
    logger.addHandler(handler);
Check code on GitHub

By default all logs are sent to sys.stderr. To direct output somewhere else, you need to add a handler with either a StreamHandler or a FileHandler:

    log_path = "selenium.log"
    handler = logging.FileHandler(log_path)
    logger.addHandler(handler)
Check code on GitHub 
.NET does not currently have a Logging implementation

By default, logs are sent to the console in stdout.
To store the logs in a file:

      logger.output = file_name
Check code on GitHub

JavaScript does not currently support sending output to a file.

To send logs to console output:

logging.installConsoleHandler()

Logger filtering

Java logging is managed on a per class level, so instead of using the root logger (Logger.getLogger("")), set the level you want to use on a per-class basis:

    Logger.getLogger(RemoteWebDriver.class.getName()).setLevel(Level.FINEST);
    Logger.getLogger(SeleniumManager.class.getName()).setLevel(Level.SEVERE);
Check code on GitHub
Because logging is managed by module, instead of working with just "selenium", you can specify different levels for different modules: 
    logging.getLogger('selenium.webdriver.remote').setLevel(logging.WARN)
    logging.getLogger('selenium.webdriver.common').setLevel(logging.DEBUG)
Check code on GitHub 
.NET does not currently have a Logging implementation

Ruby’s logger allows you to opt in (“allow”) or opt out (“ignore”) of log messages based on their IDs. Everything that Selenium logs includes an ID. You can also turn on or off all deprecation notices by using :deprecations.

These methods accept one or more symbols or an array of symbols:

      logger.ignore(:jwp_caps, :logger_info)
Check code on GitHub

or

      logger.allow(%i[selenium_manager example_id])
Check code on GitHub