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Slint tests

This documents describe the testing infrastructure of Slint

Syntax tests

The syntax tests are testing that the compiler show the right error messages in case of error.

The syntax tests are located in internal/compiler/tests/syntax/ and it's driven by the syntax_tests.rs file. More info in the comments of that file.

In summary, each .slint files have comments with > <error like so:

foo bar
//  > <error{parse error}

Meaning that there must be an error on the line above spanning bar, as indicated by the > and < arrows.

Ideally, each error message must be tested like so.

The syntax test can be run alone with

cargo test -p i-slint-compiler --features display-diagnostics --test syntax_tests

In order to update the failing tests, set the SLINT_SYNTAX_TEST_UPDATE environment variable to 1.

SLINT_SYNTAX_TEST_UPDATE=1 cargo test -p i-slint-compiler --test syntax_tests

This will change the comments to add the error of the expected messages

Driver tests

These tests make sure that feature in .slint behave as expected. All the .slint files in the sub directories are going to be test by the drivers with the different language frontends.

The .slint code contains a comment with some block of code which is extracted by the relevant driver.

Interpreter test

The interpreter test is the faster test to compile and run. It test the compiler and the eval feature as run by the viewer or such. It can be run like so:

cargo test -p test-driver-interpreter --

You can add an argument to test only for particular tests.

If the last component in the file includes a bool property named test, the test will verify that its value is true.

example:

export component Foo inherits Rectangle {
   // test would fail if that property was false
   in-out property <bool> test: 1 + 1 == 2;
}

Rust driver

The rust driver will compile each snippet of code and put it in a slint! macro in its own module In addition, if there are ```rust blocks in a comment, they are extracted into a #[test] function in the same module. This is useful to test the rust api. The SLINT_TEST_FILTER environment variable can be set while building to only build the tests that matches the filter. Example: to run all the layout tests:

SLINT_TEST_FILTER=layout cargo test -p test-driver-rust

or

tests/run_tests.sh rust layout

Instead of putting everything in a slint! macro, it's possible to tell the driver to do the compilation in the build.rs, with the build-time feature:

SLINT_TEST_FILTER=layout cargo test -p test-driver-rust --features build-time

or

tests/run_tests.sh rust layout --features build-time

C++ driver

The C++ test driver will take each .slint and generate a .h for it. It will also generate a .cpp that includes it, and add the ```cpp block in the main function. Each program is compiled separately. And then run.

Some macro like assert_eq are defined to look similar to the rust equivalent.

cargo test -p  test-driver-cpp --

Note that there are also C++ unit tests that can be run by CMake

Node driver

This is used to test the NodeJS API. It takes the ```js blocks in comment and make .js file with it that loads the .slint and runs node with it. Each test is run in a different node process.

cargo  test -p test-driver-nodejs

Screenshot tests

This is used to test renderer backends. At the moment it supports the SoftwareRenderer. Each .slint file in tests/screenshots/cases will be loaded rendered and the results will be compared to the reference images in tests/screenshots/references.

To generate references images for all test files in tests/screenshots/cases run:

SLINT_CREATE_SCREENSHOTS=1 cargo test -p test-driver-screenshots

To start the tests run and compare images:

cargo test -p test-driver-screenshots

Embedded MCP Server

The testing backend includes an embedded MCP (Model Context Protocol) server that allows AI coding tools (e.g. Claude Code) to inspect and interact with a running Slint application in real time. Enable the mcp Cargo feature on i-slint-backend-selector and set the SLINT_MCP_PORT environment variable to start the server.

See the testing backend README for usage instructions and docs/development/mcp-server.md for architecture details.

Doctests

cargo test -p doctests

The doctests extracts the ```slint from the files in the docs folder and make sure that the snippets can be build without errors