# TestThreads

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](Placeholders.html).                                                                                                                |
| TestAffinity      | Optional          | Defines a filter applied to tests run in this thread. Only tests with the specified tag are executed in the thread.<br>**Example:** `<TestAffinity>testpath:Target:FireFox</TestAffinity>` only executes tests with the `FireFox` tag in the thread. |

You can use the `{TestThreadId}` as a [placeholder](Placeholders.md) 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.

## Example

```xml
<TestThreads>
    <TestThread id="0">
        <TestAffinity>testpath:Target:FireFox</TestAffinity>
    </TestThread>
</TestThreads>
```