Crate macrotest

  Test harness for macro expansion.

Similar to trybuild, but allows you to write tests on how macros are expanded.

Macro expansion tests

A minimal macrotest setup looks like this:

#[test]
pub fn pass() {
    let t = macrotest::TestCases::new();
    t.pass("tests/expand/*.rs");
}

The test can be run with cargo test. It will individually extract each of the source files matches the glob pattern as main.rs in a separate cargo crate in temporary folder and will invoke cargo expand to expand macro invocations.

Project's crate will listed under [dependencies] section of temporary crates and will be available from the test cases.

Expansion result is compared with the corresponding .expanded.rs file (same file name as the test except with a different extension). If file doesn't exists, it will create a new one (this is how you update your tests).

Possible test outcomes are:

• Pass: expansion succeeded and result is the same as in .expanded.rs file
• Fail: expansion is different from the .expanded.rs file content. This will print a diff
• Refresh: .expanded.rs didn't exist and has been created

NB: after execution of each test, a temporary folder with the crate is removed automatically.

Workflow

First of all, the cargo-expand tool must be present. You can install it via cargo:

cargo install cargo-expand

A nigthly compiler is required for this tool to operate, so it must be installed as well.

Setting up a test project

Inside your crate that provides procedural or declarative macros, create a test case under tests directory.

Under the tests directory create an expand directory and populate it with different expansion test cases as Rust source files.

Then, udner the tests directory, create tests.rs file that will run the tests:

#[test]
pub fn pass() {
    let t = macrotest::TestCases::new();
    t.pass("tests/expand/*.rs");
}

And then you can run cargo test to

1. For the first time, generate the .expanded.rs files for each of the test cases under the expand directory
2. After that, test cases' expansion result will be compared with the content of .expanded.rs files

Updating .expanded.rs

Just remove the .expanded.rs files and re-run the corresponding tests. Files will be created automatically; hand-writing them is not recommended.

Modules

common

Structs

TestCases

Enums

Error