# How to Run Tests in Automattic/harper: Complete Guide for Rust Core and Extensions > Master running tests in Automattic/harper with this comprehensive guide. Learn to execute Rust unit tests, WASM builds, and Playwright integration tests using the unified justfile. - Repository: [Automattic/harper](https://github.com/Automattic/harper) - Tags: how-to-guide - Published: 2026-07-26 --- **The Harper repository uses a unified `justfile` to orchestrate Rust unit tests, WebAssembly builds, and Playwright-based integration tests for the VS Code extension, Obsidian plugin, and browser extensions.** Automattic/harper is a grammar checker built with a Rust core engine and TypeScript/JavaScript frontends. The test suite spans the Rust-based language server (`harper-ls`), the WebAssembly-powered JavaScript library, and multiple editor extensions. All testing is coordinated through the `justfile` at the repository root, providing consistent commands for local development and CI pipelines. ## Run the Complete Test Suite To execute every test target in the correct order, use the top-level test recipe. This runs Rust unit tests, builds WebAssembly artifacts, and triggers Playwright suites for all supported platforms: ```bash just test ``` According to the `justfile` (lines 99-100), this recipe bundles all individual test tasks together to ensure the entire workspace validates correctly. ## Test the Rust Core and Language Server Harper’s core engine, command-line interface, and language server protocol (LSP) implementation live in the Rust workspace. Run these unit and integration tests using Cargo: ```bash just test-rust ``` Internally, the `test-rust` recipe executes `cargo test -q` across the entire workspace (lines 94-96), covering crates like `harper-core` and `harper-ls`. For example, core linting logic is validated in [`harper-core/tests/linters.rs`](https://github.com/Automattic/harper/blob/main/harper-core/tests/linters.rs) using standard Rust test assertions. ## Test the WebAssembly JavaScript Wrapper (Harper.js) Harper.js provides the WebAssembly-based JavaScript API. Its test suite validates the WASM bundle and browser compatibility: ```bash just test-harperjs ``` This recipe first calls `build-harperjs` to compile the Rust source to WASM, installs Node dependencies with `pnpm`, runs Playwright tests, and launches the example runner to verify the demo application functions correctly (lines 104-116). ## Test Editor Extensions The VS Code and Obsidian extensions require the compiled language server binary or WASM artifacts to test correctly. ### VS Code Extension The VS Code extension tests depend on the `harper-ls` binary being present in the extension's `bin/` directory. The test flow defined in the `test-vscode` target (lines 30-57) rebuilds the binary in release mode, copies it to the correct location, installs Node dependencies, and executes the extension test suite: ```bash just test-vscode ``` On Linux CI environments, this runs under headless Xvfb to simulate a display server. The `justfile` handles all prerequisite steps automatically. ### Obsidian Plugin For the Obsidian plugin, tests validate the integration between the TypeScript plugin code and the WebAssembly core: ```bash just test-obsidian ``` This target builds the required WASM bundle, installs the plugin's dependencies, and runs Playwright tests against the Obsidian plugin environment (lines 18-26). ## Test Browser Extensions Harper provides extensions for Chrome and Firefox that rely on the compiled WebAssembly module and extension assets. ### Chrome Extension Run the Chrome extension tests with: ```bash just test-chrome-plugin ``` The recipe first builds the Chrome plugin assets and WASM bundle, installs dependencies, then invokes Playwright (lines 91-107). On Linux systems, it automatically wraps the execution with Xvfb for headless CI compatibility. ### Firefox Extension Firefox extension testing follows an identical pattern: ```bash just test-firefox-plugin ``` This builds the Firefox-specific plugin, installs dependencies, and runs Playwright with the same Xvfb handling used for Chrome testing on Linux CI runners (lines 110-124). ## Summary - **`just test`** runs the entire test suite across Rust, JavaScript, and all extension platforms in the correct dependency order. - **Rust tests** use `cargo test -q` and cover the core engine and language server in `harper-core/tests/` and related crates. - **Harper.js tests** require WASM compilation and run via Playwright to validate the WebAssembly API. - **Extension tests** for VS Code, Obsidian, Chrome, and Firefox use Playwright and automatically rebuild their binary or WASM dependencies before execution. - Most recipes handle prerequisite builds automatically, so you can run individual test targets without manual compilation steps. ## Frequently Asked Questions ### What testing framework does Harper use for Rust code? Harper uses the standard Rust testing framework via `cargo test`. The workspace contains unit and integration tests in crates like `harper-core`, with test files located in [`harper-core/tests/linters.rs`](https://github.com/Automattic/harper/blob/main/harper-core/tests/linters.rs) and similar directories. The `just test-rust` command runs `cargo test -q` across the entire workspace according to the `justfile` implementation. ### Do I need to build WebAssembly or the language server before running tests? No. The `justfile` recipes automatically handle dependency builds. For example, `just test-harperjs` invokes `build-harperjs` first, and `just test-vscode` rebuilds `harper-ls` in release mode before copying it to the extension directory. You can invoke test targets directly without manual build steps. ### How do I run only the VS Code extension tests? Use `just test-vscode` to run only the VS Code extension test suite. This command compiles the `harper-ls` binary in release mode, copies it to `packages/vscode-plugin/bin/`, installs Node dependencies, and runs the extension tests. It handles Linux headless environments automatically using Xvfb when necessary. ### Why do some tests require Xvfb on Linux? Browser and VS Code extension tests use Playwright to automate UI interactions that require a display server. On Linux CI environments where no display is available, the `justfile` wraps these tests with Xvfb (X Virtual Framebuffer) to provide a virtual display. This is handled automatically in the `test-vscode`, `test-chrome-plugin`, and `test-firefox-plugin` recipes when running on Linux.