Testing Basics

If you're new to Rust, you'll want to review these important tools to help you build tests.

The assert! macro

You can use the assert! macro to assert certain conditions in your test. This macro invokes panic!() and fails the test if the expression inside evaluates to false.

assert!(value == 5);

The assert_eq! macro

The assert_eq! macro works a lot like the assert macro, however instead it accepts two values, and panics if those values are not equal.

assert_eq!(balance, 100);

The assert_ne! macro

The assert_ne! macro works just like the assert_eq! macro, but it will panic if the two values are equal.

assert_ne!(address, 0);

The println! macro

You can use the println! macro to print values to the console.

println!("WALLET 1 ADDRESS {}", wallet_1.address());
println!("WALLET 1 ADDRESS {:?}", wallet_1.address());

Using {} will print the value, and using {:?} will print the value plus its type.

Using {:?} will also allow you to print values that do not have the Display trait implemented but do have the Debug trait. Alternatively you can use the dbg! macro to print these types of variables.

println!("WALLET 1 PROVIDER {:?}", wallet_1.provider().unwrap());
dbg!("WALLET 1 PROVIDER {}", wallet_1.provider().unwrap());

To print more complex types that don't have it already, you can implement your own formatted display method with the fmt module from the Rust standard library.

use std::fmt;

struct Point {
    x: u64,
    y: u64,

// add print functionality with the fmt module 
impl fmt::Display for Point {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "value of x: {}, value of y: {}", self.x, self.y)

let p = Point {x: 1, y: 2};
println!("POINT: {}", p);

Run Commands

You can run your tests to see if they pass or fail with

cargo test

Outputs will be hidden if the test passes. If you want to see outputs printed from your tests regardless of whether they pass or fail, use the nocapture flag.

cargo test -- --nocapture