insta: a snapshot testing library for Rust
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[](https://crates.io/crates/insta)
[](https://github.com/mitsuhiko/insta/blob/master/LICENSE)
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[](https://docs.rs/insta)
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## Introduction
Snapshots tests (also sometimes called approval tests) are tests that
assert values against a reference value (the snapshot). This is similar
to how `assert_eq!` lets you compare a value against a reference value but
unlike simple string assertions, snapshot tests let you test against complex
values and come with comprehensive tools to review changes.
Snapshot tests are particularly useful if your reference values are very
large or change often.
## Example
```rust
#[test]
fn test_hello_world() {
insta::assert_debug_snapshot!(vec![1, 2, 3]);
}
```
Curious? There is a screencast that shows the entire workflow: [watch the insta
introduction screencast](https://www.youtube.com/watch?v=rCHrMqE4JOY&feature=youtu.be).
Or if you're not into videos, read the [5 minute introduction](https://insta.rs/docs/quickstart/).
Insta also supports inline snapshots which are stored right in your source file
instead of separate files. This is accomplished by the companion
[cargo-insta](https://github.com/mitsuhiko/insta/tree/master/cargo-insta) tool.
## Editor Support
For looking at `.snap` files there is a [vscode extension](https://github.com/mitsuhiko/insta/tree/master/vscode-insta)
which can syntax highlight snapshot files, review snapshots and more. It can be installed from the
marketplace: [view on marketplace](https://marketplace.visualstudio.com/items?itemName=mitsuhiko.insta).
## Diffing
Insta uses [`similar`](https://github.com/mitsuhiko/similar) for all its diffing
operations. You can use it independently of insta. You can use the
[`similar-asserts`](https://github.com/mitsuhiko/similar-asserts) crate to get
inline diffs for the standard `assert_eq!` macro to achieve insta like diffs
for regular comparisons:
```rust
use similar_asserts::assert_eq;
fn main() {
let reference = vec![1, 2, 3, 4];
assert_eq!(reference, (0..4).collect::