rust/docs/TESTS.md

libsyntax2.0 testing infrastructure

Libsyntax2.0 tests are in the tests/data directory. Each test is a pair of files, an .rs file with Rust code and a .txt file with a human-readable representation of syntax tree.

The test suite is intended to be independent from a particular parser: that's why it is just a list of files.

The test suite is intended to be progressive: that is, if you want to write a Rust parser, you can TDD it by working through the test in order. That's why each test file begins with the number. Generally, tests should be added in order of the appearance of corresponding functionality in libsytnax2.0. If a bug in parser is uncovered, a new test should be created instead of modifying an existing one: it is preferable to have a gazillion of small isolated test files, rather than a single file which covers all edge cases. It's okay for files to have the same name except for the leading number. In general, test suite should be append-only: old tests should not be modified, new tests should be created instead.

Note that only ok tests are normative: err tests test error recovery and it is totally ok for a parser to not implement any error recovery at all. However, for libsyntax2.0 we do care about error recovery, and we do care about precise and useful error messages.

There are also so-called "inline tests". They appear as the comments with a test header in the source code, like this:

// test fn_basic
// fn foo() {}
fn fn_item(p: &mut Parser) {
    // ...
}

You can run cargo collect-tests command to collect all inline tests into tests/data/inline directory. The main advantage of inline tests is that they help to illustrate what the relevant code is doing.

Contribution opportunity: design and implement testing infrastructure for validators.