# autospy
[](./LICENSE)
A test spy object library.
## Overview
Spies are a type of [test double](https://en.wikipedia.org/wiki/Test_double) used for unit testing software. A test spy is an object providing the same interface as the production code, but which allows setting of the output before a test runs and verification of input parameters after the test run.
## Usage
Spy objects are often only used by unit tests, the example below demonstrates use in a unit test.
```rust
use autospy::autospy;
#[cfg_attr(test, autospy)]
trait MyTrait {
fn foo(&self, x: u32) -> bool;
}
fn use_trait<T: MyTrait>(trait_object: T) -> bool {
trait_object.foo(10)
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn test_trait() {
let spy = MyTraitSpy::default();
spy.foo.returns.push_back(true);
assert!(use_trait(spy.clone()));
assert_eq!(vec![10], spy.foo.arguments.take_all())
}
}
```
## 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 much the same features. Autospy aims to offer these same features through a macro generated spy object, rather than a mock object. The use of either is largely personal preference; however, there are some benefits to using a spy object. Notably, a mock object will panic if its expectations fail which can cause less legible error messages.