📸 assert-snap

A snapshot testing and assertion library for Rust that supports flexible, regex-based dynamic data redactions and detailed unified diff output.

✨ Features

🎯 assert_snap!: Assert any types implementing Display.
🔍 assert_debug_snap!: Assert any types implementing Debug.
🛡️ Regex Redactions: Inline rules to scrub volatile data (timestamps, UUIDs, secret tokens, memory addresses) before checking assertions.
📊 Unified Diff: Built-in diff printing powered by similar on assertion failures (enabled via the diff feature, default ON).

🚀 Quickstart

Basic String Assertion (`assert_snap!`)

use assert_snap::assert_snap;

let actual_output = "User connected successfully";
let expected_snapshot = "User connected successfully";

assert_snap!(actual_output, expected_snapshot);

Debug Assertion (`assert_debug_snap!`)

use assert_snap::assert_debug_snap;

#[derive(Debug)]
struct User {
    id: u64,
    name: String,
}

let user = User { id: 42, name: "Alice".into() };

assert_debug_snap!(
    user,
    User {
        id: 42,
        name: "Alice".to_string(),
    }
);

🛡️ Redacting Dynamic Data

Dynamic values like generated IDs, secret keys, or timestamps can cause snapshot test instability. assert-snap allows appending redaction rules directly inside the macro invocation.

Basic Redaction Syntax

Format: "regex_pattern" => "replacement" (redacts all matches)

use assert_snap::assert_snap;

let actual = "Response time: 142ms, status: 200";
let expected = "Response time: [DURATION], status: 200";

assert_snap!(
    actual,
    expected,
    r"\d+ms" => "[DURATION]"
);

Redactions with Limits

Format: [limit] "regex_pattern" => "replacement"

By default (or with [0]), all matches are redacted. Specifying a limit (e.g., [1]) restricts redaction to that maximum number of matches:

use assert_snap::assert_snap;

let actual = "token: secret_abc, session: secret_xyz";
let expected = "token: ****, session: secret_xyz";

assert_snap!(
    actual,
    expected,
    [1] "secret_[a-z]+" => "****"
);

Multiple Redaction Rules

You can combine multiple redaction rules separated by commas:

use assert_snap::assert_debug_snap;

#[derive(Debug)]
struct Session {
    id: String,
    token: String,
    active: bool,
}

let session = Session {
    id: "sess-98765".into(),
    token: "Bearer secret-token-123".into(),
    active: true,
};

assert_debug_snap!(
    session,
    Session {
        id: "sess-****".to_string(),
        token: "Bearer ****".to_string(),
        active: true,
    },
    r"sess-\d+" => "sess-****",
    r"Bearer .+" => "Bearer ****"
);

⚙️ Cargo Features

Feature	Default	Description
`diff`	Enabled	Prints a unified diff using the `similar` crate when an assertion fails.

To disable default features (such as diff to minimize dependencies):

[dependencies]
assert-snap = { version = "0.0.0", default-features = false }

📜 License

This project is dual-licensed under:

You may choose either license at your discretion.

🤝 Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual-licensed as above, without any additional terms or conditions.

assert-snap 0.0.1