Slint UI Testing with Python

Use the Slint UI Testing module to launch a Slint application locally or on a remote machine via SSH, inspect its UI, trigger actions, and verify correct behaviour.

This documentation describes slint_testing 0.6.1.

Prerequisites

Python 3 ↗
uv ↗
Slint 1.17 or newer.

Your application needs to be built with system testing support:

For Rust applications, enable the system-testing feature of the slint crate.
For C++ applications, set SLINT_FEATURE_SYSTEM_TESTING=ON in your CMake configuration.

In addition, the SLINT_EMIT_DEBUG_INFO=1 environment variable must be set during the application build process. We anticipate that this requirement will be lifted in favor of an easier mechanism in the future.

Installation

slint_testing is distributed through Slint’s package index at testing.slint.dev. With your license you receive an access token.

Give the token to uv, once per machine:
Terminal window
```
uv auth login https://testing.slint.dev/simple/ --token <TOKEN>
```
uv remembers it for testing.slint.dev, so it never appears in your project.
Point your project at Slint’s index for slint-testing only, in pyproject.toml:
```
[[tool.uv.index]]
name = "slint-private"
url = "https://testing.slint.dev/simple/"
explicit = true

[tool.uv.sources]
slint-testing = { index = "slint-private" }
```
explicit = true keeps PyPI as the default for everything else. The URL holds no token, so commit this even if your repository is public.
Add the package:
Terminal window
```
uv add slint-testing
```

Continuous integration

Store the token as a repository secret. uv reads the credentials for an index from environment variables named after it (slint-private → SLINT_PRIVATE), so no uv auth login is needed. For GitHub Actions:

- uses: astral-sh/setup-uv@v6
  with:
    enable-cache: true
- run: uv sync
  env:
    UV_INDEX_SLINT_PRIVATE_USERNAME: __token__
    UV_INDEX_SLINT_PRIVATE_PASSWORD: ${{ secrets.SLINT_TESTING_TOKEN }}

For a complete workflow that runs tests on Linux, macOS, and Windows, see the CI workflow ↗ of the examples.

Token in the index URL

The token also works in the index URL, https://testing.slint.dev/t/<TOKEN>/, without uv auth login. uv then writes that URL, token included, into uv.lock, so keep it out of public repositories.

Usage

import slint_testing

with slint_testing.Application(["/path/to/my_app"]) as aut:
    window = aut.first_window

    root_element = window.root_element
    celsius_field = root_element.query_descendants().match_id("App::celsius-input").find_first()
    convert_button = root_element.query_descendants().match_id("App::convert-button").find_first()
    fahrenheit_field = root_element.query_descendants().match_id("App::fahrenheit-input").find_first()

    celsius_field.accessible_value = "100"
    convert_button.invoke_accessible_default_action()

    assert fahrenheit_field.accessible_value == "212"

The slint_testing module provides an Application class, which wraps the Application Under Test (AUT). Construct it with the command line arguments needed to launch the compiled application, and use it with Python’s with ↗ statement. Before entering your block, the application is launched and slint_testing waits until the first window is shown and connected.

Fetch the Window from the Application, and then its root_element. Use query_descendants to initiate a query into the entire tree of elements, refine it for example via match_id and finally obtain Element references to the UI elements by calling find_first or find_all.

Use Element‘s API to change state via accessible actions, verify size and position, as well as accessible properties.

Examples

The ui-testing-examples ↗ repository contains example applications written in Rust, C++, Node.js, and Python, each with a suite of tests. They show how to build an application with system testing support, launch it from pytest fixtures, and find and interact with elements. Each example is self-contained, so you can copy its directory as a starting point for your own project.

Networking

The slint_testing module and the AUT are connected via a TCP connection and exchange messages. slint_testing creates a listening TCP socket and passes the address to the AUT via the SLINT_TEST_SERVER environment variable. The AUT, when enabled for system testing, will automatically attempt to connect to the listening TCP socket when the first window is shown. This assumes readiness of the application, similar to how visibility on the screen indicates readiness to an end-user.

When launched via SSH, slint_testing configures SSH to open a listening socket on the remote side at port 8091 and configures a remote tunnel to forward to the local socket slint_testing created.