63 lines
2.6 KiB
Markdown
63 lines
2.6 KiB
Markdown
---
|
|
title: Testing tricks in Rust
|
|
date: 2018-09-25 00:00:00
|
|
tags: [rust, tdd, testing]
|
|
series: rust-testing-tricks
|
|
---
|
|
|
|
# Use verbs as test module names
|
|
|
|
Who said that the test module needs to be named `test` ?
|
|
Experiment with different module names, pay attention to how the test runner displays the results.
|
|
|
|
A structure that I like, an example:
|
|
|
|
`worker.rs:`
|
|
|
|
```rust
|
|
// some production code here
|
|
|
|
mod should {
|
|
|
|
#[test]
|
|
fn consume_message_from_queue() {
|
|
// mock queue, create worker with that queue injected
|
|
// start worker
|
|
// check if queue's 'get_message' was invoked
|
|
}
|
|
|
|
}
|
|
```
|
|
|
|
Cargo prints `worker::should::consume_message_from_queue` when running this test, which reads nicely and exposes the requirement.
|
|
|
|
# Interior mutability for controlling state of variables injected from the test
|
|
|
|
Use e.g. the `atomic` types family or `RefCell` itself to get an immutable handle to a internally mutable data.
|
|
Useful when you don't want your production code to accept anything that can mutate but you still want to control that value from the test.
|
|
|
|
See injecting the system clock example in [my previous blog post](/posts/2018/07/rust-injection.html).
|
|
|
|
# Write the test first
|
|
|
|
Not really a Rust trick, but hey.
|
|
Try writing your test first, before production code.
|
|
If you're building a feature or fixing a bug that will affect external behaviour - start with an integration test at the crate level.
|
|
|
|
Try thinking what would be the ideal code you would like to interact with, what would be the types, what would be the functions ? A broad-strokes scenario, not caring much about implementation details, not caring much about covering all edge cases. Write that code. It does not compile. But it looks nice, you're pleased.
|
|
|
|
Read through again, add assertions. Add the types. For each missing feature or a bug that is present in this high level scenario - write a unit test. Satisfy that test with changes to production code. Maybe refactor a bit in between. Once the big test is green - you're done !
|
|
|
|
There is no Rust-focused TDD book just yet for me to recommend, but here, have some for other languages:
|
|
|
|
- Kent Beck - Test Driven Development: By Example
|
|
- Steve Freeman, Nat Pryce - Growing Object-Oriented Software, Guided by Tests
|
|
|
|
Rust allows for more cool tricks and generally writing less test code than mentioned in these books, so please use your judgment - and the tricks from this article !
|
|
|
|
# Let's talk !
|
|
|
|
Have any questions ? Would like to pair on Rust ? Curious about TDD ? Ping me !
|
|
Email is good - [hello@cyplo.net](mailto:hello@cyplo.net) or try [Twitter](https://twitter.com/cyplo).
|
|
|
|
thanks !
|