# autospy
###### *🎵 autospy record, autospy replace 🎵*
[](https://crates.io/crates/autospy)
[](https://docs.rs/autospy/latest/autospy/)
[](https://github.com/lhalf/autospy/actions/workflows/on_commit.yml)
[](./LICENSE)
A test spy object library.
## Overview
A test spy is a type of [test double](https://en.wikipedia.org/wiki/Test_double) used in unit testing. It provides the same
interface as the production code, but allows you to set outputs before use in a test
and to verify input parameters after the spy has been used.
[`#[autospy]`](https://docs.rs/autospy/latest/autospy/) generates a test spy object for traits.
## Usage
The example below demonstrates use in a unit test assuming `autospy` is included in `[dev-dependencies]`.
```rust
#[cfg_attr(test, autospy::autospy)]
trait MyTrait {
fn foo(&self, x: u32) -> bool;
}
fn use_trait(trait_object: impl MyTrait) -> bool {
trait_object.foo(10)
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_trait() {
let spy = MyTraitSpy::default(); // build spy
spy.foo.returns.set([true]); // set the return values
assert!(use_trait(spy.clone())); // use the spy
assert_eq!([10], spy.foo.arguments) // check the captured arguments
}
}
```
For additional examples and features see the [docs](https://docs.rs/autospy).
## Acknowledgements
Autospy is heavily influenced by the excellent [mockall](https://docs.rs/mockall/latest/mockall/) crate, which,
through [automock](https://docs.rs/mockall/latest/mockall/attr.automock.html), provides many similar features.
Autospy aims to offer these features through a macro-generated spy object, rather than a mock object. The use of either is
largely personal preference; however, there are some advantages to using a spy object:
| Mock | Panics if expectations fail; error messages can be unclear | Less standard pattern, expectations are baked into object | More crate-specific syntax and usage patterns |
| Spy | Asserts like any regular test | Assert after use, more standard test pattern | Simple: set what's returned, then inspect what was called |