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tests/wpt/web-platform-tests/docs/writing-tests/wdspec.md

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+# wdspec tests
+
+The term "wdspec" describes a type of test in WPT which verifies some aspect of
+[the WebDriver protocol](https://w3c.github.io/webdriver/). These tests are
+written in [the Python programming language](https://www.python.org/) and
+structured with [the pytest testing
+framework](https://docs.pytest.org/en/latest/).
+
+The test files are organized into subdirectories based on the WebDriver
+command under test. For example, tests for [the Close Window
+command](https://w3c.github.io/webdriver/#close-window) are located in then
+`close_window` directory.
+
+Similar to [testharness.js](testharness) 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](https://w3c.github.io/webdriver/#element-click):
+
+```python
+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(
+            session_id=session.session_id,
+            element_id=element.id))
+
+    assert_success(response)
+```
+
+## 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](https://docs.pytest.org/en/latest/fixture.html).