# rust-passert

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Pretty/Power assertion macros for rust

## Overview

An assert macro in the spirit of
[Spock/Groovy assertions]
(http://docs.groovy-lang.org/latest/html/documentation/core-testing-guide.html#_power_assertions) which evaluates and prints subexpressions,
simplifying failure analysis

## Example

```rust
#![feature(plugin)]
#![plugin(passert_macros)]

extern crate passert;

#[test]
#[should_panic]
fn it_works() {
    let a = 3;
    let b = 4;
    passert!(a + 2 + 3 == -b);
}
```

Output


```
running 1 test
Assertion failed:
a + 2 + 3 == -b
| |   |   |  ||
3 5   8   |  |4
          |  -4
          false
thread 'it_works' panicked at 'Assertion failed: a + 2 + 3 == -b', src/lib.rs:11

```

## Limitations/Caveats

 - All displayed subexpressions must implement `Debug`.
 - The transformation of subexpression to strings via `Debug` is done _after_ the whole expression
   has been evaluated. In cases where other subexpressions cause changes to previously
   evaluated subexpression the displayed value may be incorrect.
 - The logical expressions `&&` and `||` are not evaluated lazily.
 - A new binding is created for each subexpression, this may have unintended side effects.