simple-rust-tests/__wasm/wit-bindgen-sample/wit-bindgen/tests

Testing wit-bindgen - `codegen

Any tests placed into the tests/codegen directory should be raw *.wit files. These files will be executed in all code generators by default most likely, and 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.

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

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 files:

• host.rs - executes wasms with Wasmtime
• host.js - executes WebAssembly with node.js
• host.py - executes with wasmtime's PyPI package.

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.

The general layout is then that if you want to run the JS host tests you run:

$ cargo test -p wit-bindgen-gen-js

and if you want to run all tests you can execute:

$ cargo test --workspace

It's all a bit convoluted so feel free to ask questions on Zulip or open an issue if you're lost.