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Testing Basics

docs/src/testing/basics.md

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Testing Basics

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

The assert! macro

<!-- This section should explain the `assert!` macro --> <!-- assert:example:start -->

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:example:end --> <!-- This section should show an example of the `assert!` macro --> <!-- assert_code:example:start -->
rust,
assert!(value == 5);
<!-- assert_code:example:end -->

The assert_eq! macro

<!-- This section should show an example of the `assert_eq!` macro --> <!-- assert_eq:example:start -->

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:example:end --> <!-- This section should show an example of the `assert_eq!` macro --> <!-- assert_eq_code:example:start -->
rust,
assert_eq!(balance, 100);
<!-- assert_eq_code:example:end -->

The assert_ne! macro

<!-- This section should show an example of the `assert_ne!` macro --> <!-- assert_ne:example:start -->

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

<!-- assert_ne:example:end --> <!-- This section should show an example of the `assert_ne!` macro --> <!-- assert_ne_code:example:start -->
rust,
assert_ne!(address, 0);
<!-- assert_ne_code:example:end -->

The println! macro

<!-- This section should explain how the `println!` macro can be used in tests --> <!--print_ln:example:start -->

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

<!--print_ln:example:end --> <!-- This section should show an example of the `println!` macro --> <!--print_ln_code:example:start -->
rust,
println!("WALLET 1 ADDRESS {}", wallet_1.address());
println!("WALLET 1 ADDRESS {:?}", wallet_1.address());
<!--print_ln_code:example:end --> <!-- This section should explain how `{}` and `{:?}` are used in the `println!` macro --> <!--print_ln_2:example:start -->

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.

<!--print_ln_2:example:end --> <!-- This section should show an example of the `println!` and `dbg` macros --> <!--print_ln_dbg_code:example:start -->
rust,
println!("WALLET 1 PROVIDER {:?}", wallet_1.provider());
dbg!("WALLET 1 PROVIDER {}", wallet_1.provider());
<!--print_ln_dbg_code:example:end --> <!-- This section should explain how implement custom fmt --> <!--fmt:example:start -->

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.

<!--fmt:example:end --> <!-- This section should show a code example of how implement custom fmt --> <!--fmt_code:example:start -->
rust,
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);
<!--fmt_code:example:end -->

Run Commands

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

shell
cargo test
<!-- This section should when outputs are hidden and what the `nocapture` flag does --> <!--outputs:example:start -->

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.

<!--outputs:example:end -->
shell
cargo test -- --nocapture