wdspec tests

The term “wdspec” describes a type of test in WPT which verifies some aspect of the WebDriver protocol. These tests are written in the Python programming language and structured with the pytest testing framework.

The test files are organized into subdirectories based on the WebDriver command under test. For example, tests for the Close Window command are located in then close_window directory.

Similar to testharness.js tests, wdspec tests contain within them any number of “sub-tests.” Sub-tests are defined as Python functions whose name begins with test_, e.g. test_stale_element.

The webdriver client library

web-platform-tests maintains a WebDriver client library called webdriver located in the tools/webdriver/ directory. Like other client libraries, it makes it easier to write code which interfaces with a browser using the protocol.

Many tests require some “set up” code–logic intended to bring the browser to a known state from which the expected behavior can be verified. The convenience methods in the webdriver library should be used to perform this task because they reduce duplication.

However, the same methods should not be used to issue the command under test. Instead, the HTTP request describing the command should be sent directly. This practice promotes the descriptive quality of the tests and limits indirection that tends to obfuscate test failures.

Here is an example of a test for the Element Click command:

from tests.support.asserts import assert_success
from tests.support.inline import inline

def test_null_response_value(session):
    # The high-level API is used to set up a document and locate a click target
    session.url = inline("<p>foo")
    element = session.find.css("p", all=False)

    # An HTTP request is explicitly constructed for the "click" command itself
    response = session.transport.send(
        "POST", "session/{session_id}/element/{element_id}/click".format(


Utility functions

The wedbdriver library is minimal by design. It mimics the structure of the WebDriver specification. Many conformance tests perform similar operations (e.g. calculating the center point of an element or creating a document), but the library does not expose methods to facilitate them. Instead, wdspec tests define shared functionality in the form of “support” files.

Many of these functions are intended to be used directly from the tests using Python’s built-in import keyword. Others (particularly those that operate on a WebDriver session) are defined in terms of Pytest “fixtures” and must be loaded accordingly. For more detail on how to define and use test fixtures, please refer to the pytest project’s documentation on the topic.