The <TestThreads> element is a container for <TestThread> elements. The following attributes are available for <TestThread> elements:

Element/Attribute Required/Optional Description
id Integer ID of the test thread (zero-indexed). This value can be accessed using the {TestThreadId} placeholder.
TestAffinity Optional Defines a filter applied to tests run in this thread. Only tests containing with the specified tag are executed in the thread.
Example: <TestAffinity>testpath:Target:FireFox</TestAffinity> only executes tests with the FireFox tag in the thread.

You can use the {TestThreadId} as a placeholder to reference the thread ID, e.g. to transform the name of the database instance you are accessing based on the thread ID, ensuring that each thread accesses a separate instance of the database. This prevents the threads from conflicting with one another when accessing the database, as thread 0 may manipulate data that is required by thread 1 otherwise.