Headless Mode Testing

[hecrj]

This PR introduces a brand new crate for headless mode testing: iced_test.

This crate features a Simulator type that can be used to simulate user interactions and query any Element produced by iced.

Basic Usage

Let's assume we want to test the classical counter interface.

First, we will want to create a Simulator of our interface:

use iced_test::simulator;

let mut counter = Counter { value: 0 };
let mut ui = simulator(counter.view());

Now we can simulate a user interacting with our interface. Let's use Simulator::click to click the counter buttons:

use iced_test::selector::text;

let _ = ui.click(text("+"));
let _ = ui.click(text("+"));
let _ = ui.click(text("-"));

Simulator::click takes a Selector. A Selector describes a way to query the widgets of an interface. In this case, selector::text lets us select a widget by the text it contains.

We can now process any messages produced by these interactions and then assert that the final value of our counter is indeed 1!

for message in ui.into_messages() {
    counter.update(message);
}

assert_eq!(counter.value, 1);

We can even rebuild the interface to make sure the counter displays the proper value with Simulator::find:

let mut ui = simulator(counter.view());

assert!(ui.find(text("1")).is_ok(), "Counter should display 1!");

And that's it! That's the gist of testing iced applications!

Simulator contains additional operations you can use to simulate more interactions—like tap_key or typewrite—and even perform snapshot testing!

[GyulyVGC]

This is a remarkable milestone for Iced.

GG Héctor 🙌

[andrewdavidmackenzie]

WDYT about me taking some of the above text (currently doc dcomments in lib.rs) and examples and adding that to the repo as a README.md?

Do you see a future in this repo...I wanted to try it for some headless use with existing tests (that open a UI), then move on to proper UI testing...

[andrewdavidmackenzie]

Also, a publish of current iced_test to crates.io would be nice:
https://crates.io/crates/iced_test is 0.0.0 not 0.1.0