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Testing wit-bindgen

There are a few pre-requisites to testing the project. You only need the language compilers that you wish to run test against.

  • WASI SDK
    • Download from wasi-sdk releases page. If you're using Windows, you need the one with mingw in its name.
    • curl -LO https://github.com/WebAssembly/wasi-sdk/releases/download/wasi-sdk-20/wasi-sdk-20.0-linux.tar.gz
    • Create an environment variable called WASI_SDK_PATH`` giving the path where you extracted the WASI SDK download, i.e., the directory containing bin/lib/share`` folders.
  • Compilers for the target language:
    • Go + TinyGo - https://tinygo.org/ (v0.27.0+)
    • Rust - wasi target: rustup target add wasm32-wasi
    • Java - TeaVM-WASI ci/download-teamvm.sh
    • C - Clang
    • C# - Dotnet 8

There are two suites of tests: codegen and runtime. To run all possible tests, across all supported languages, ensure the dependency above are installed then run:

cargo test --workspace

To run just codegen tests for a single language (replace rust with language of choice: go, c, csharp, etc.):

cargo test -p wit-bindgen-rust

To run just codegen tests for a single language (replace rust with language of choice: go, c, csharp, etc.) and a single wit file (replace flags with whatever wit file should be tested):

cargo test -p wit-bindgen-rust -- flags

To run just runtime tests for a single language (replace rust with language of choice: go, c, csharp, etc.):

cargo test -p wit-bindgen-cli --no-default-features -F rust

Read on to learn more about the testing layout. It's all a bit convoluted so feel free to ask questions on Zulip or open an issue if you're lost.

Testing wit-bindgen - codegen

Any tests placed in to the tests/codegen directory should follow either of the following formats:

  1. *.wit files that are raw wit files that should be executed by the code generator.
  2. wit package in it's own directory which must contain a wit subdirectory with *.wit files and deps in it. (e.g. see tests/codegen/issue569)

The purpose of these files is to execute language-specific validation for each bindings generator. Basically if there's a bug where something generates invalid code then this is probably where the test should go. Note that this directory can have whatever it wants since nothing implements the interfaces or tries to call them.

It also contains git submodules for the wasi proposals like wasi-http.

The tests are generated by a macro codegen_tests in crates/test-helpers.

Testing wit-bindgen - runtime

Otherwise tests are organized in tests/runtime/*. Inside this directory is a directory-per-test. These tests are somewhat heavyweight so you may want to extend existing tests, but it's also fine to add new tests at any time.

The purpose of this directory is to contain code that's actually compiled to wasm and executed on hosts. The code compiled-to-wasm can be one of:

  • wasm.rs - compiled with Rust to WebAssembly
  • wasm.c - compiled with Clang
  • wasm.java - compiled with TeaVM-WASI
  • wasm.cs - compiled with NativeAOT and Mono

Existence of these files indicates that the language should be supported for the test, and if a file is missing then it's skipped when running other tests. Each wasm.* file is run inside each of the host file under tests/runtime directory.

For example, tests/runtime/variants.rs is the host file for tests/runtime/variants/

Each of these hosts can also be omitted if the host doesn't implement the test or something like that. Otherwise for each host that exists when the host's crate generator crate is tested it will run all these tests.

Testing Layout

If you're adding a test, all you should generally have to do is edit files in tests/runtime/*. If you're adding a new test it should be along the lines of just dropping some files in there, but currently if you're adding a Rust-compiled-to-wasm binary you'll need to edit crates/test-rust-wasm/Cargo.toml and add a corresponding binary to crates/test-rust-wasm/src/bin/*.rs (in the same manner as the other tests). Other than this though all other generators should automatically pick up new tests.

The actual way tests are hooked up looks roughly like:

  • All generator crates have a codegen.rs and a runtime.rs integration test file (typically defined in the crate's own tests/*.rs directory).
  • All generator crates depend on crates/test-helpers. This crate will walk the appropriate directory in the top-level tests/* directory.
  • The test-helpers crate will generate appropriate #[test] functions to execute tests. For example the JS generator will run eslint or tsc. Rust tests for codegen are simply that they compile.
  • The test-helpers crate also builds wasm files at build time, both the Rust and C versions. These are then encoded into the generated #[test] functions to get executed when testing.