baselines.md

Baselines

Baseline tests are effectively large folder-based snapshot tests. Like fourslash, these tests are somewhat integration level. These test generally test the internals of the compiler, they do this by you creating a TypeScript file where the snapshot result is a symbol map of all the symbols in that file and a list of all raised errors then compiling the tests.

How to make a baseline

1. Make a new file: touch tests/cases/compiler/overloadFunctionsNotEqualToGenerics.ts. Add some TypeScript to it.
2. d

How to amend a baseline

gulp runtests will run all the baselines eventually. Or gulp runtests -i --tests=baseline should speed things up if you only want to see those specific changes.

All of the baselines exist in tests/baselines/local/. They kinda look like:

$ tree tests/baselines/local/
tests/baselines/local/
└── api
    ├── tsserverlibrary.d.ts
    └── typescript.d.ts

1 directory, 2 files

This lets you know that two tests have changed from what you expect. They live in local/api, so you can compare the folders. I normally use Kaleidoscope, but the team loves Beyond Compare - it's a bit Windows-y but does a good job showing you how the folder infrastructure differs.

Once you're happy with the new baselines, you can run gulp baseline-accept to move them into the codebase. You will be able to see your diffs in git now. 👍