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30 lines
1.4 KiB
Markdown
30 lines
1.4 KiB
Markdown
## How tests work
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The babel-compat tests are mostly written as fixtures, similar to the [@babel/parser tests](https://github.com/babel/babel/tree/main/packages/babel-parser/test/fixtures). The `src/convert.rs` test runner looks in the `fixtures/` directory for input and expected output files. Input files are parsed into an swc AST and converted to a Babel AST in Rust. Output files are parsed directly into a Babel AST. The two ASTs are then compared, with any differences causing the test to fail.
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## How to write a test
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**Step 1**: Create a new fixture dir and input file.
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```bash
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mkdir fixtures/my-test
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echo "var a = true;" > fixtures/my-test/input.js
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```
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**Step 2**: Generate an output file with the expected Babel AST as JSON. There's a utility script available to help, but you can do this however you like.
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```bash
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# If using the babelgen.js utility, run `npm install` first to get @babel/parser dependency.
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node babelgen.js fixtures/my-test/input.js > fixtures/my-test/output.json
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```
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**Step 3**: `cargo test` should now pick up your new test automatically.
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> There's a small, insignificant different between the default Babel AST and the converted one causing my test to fail.
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This happens a lot with `None` and `Some(false)`. You'll probably want to add a normalizer function to the Normalizer visitor in `src/normalize/mod.rs`.
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## Other random utlities
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- `swcgen.js`: Prints the swc AST as JSON.
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- `compare.sh`: prints the Babel and swc ASTs side-by-side.
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