Now that we have our Rust implementation of the Game of Life rendering in the browser with JavaScript, let's talk about testing our Rust-generated WebAssembly functions.

We are going to test our tick function to make sure that it gives us the output that we expect.

Next, we'll want to create some setter and getter functions inside our existing impl Universe block in the wasm_game_of_life/src/lib.rs file. We are going to create a set_width and a set_height function so we can create Universes of different sizes.

# #![allow(unused_variables)]
#fn main() {
#[wasm_bindgen]
impl Universe { 
    // ...

    /// Set the width of the universe.
    ///
    /// Resets all cells to the dead state.
    pub fn set_width(&mut self, width: u32) {
        self.width = width;
        self.cells = (0..width * self.height).map(|_i| Cell::Dead).collect();
    }

    /// Set the height of the universe.
    ///
    /// Resets all cells to the dead state.
    pub fn set_height(&mut self, height: u32) {
        self.height = height;
        self.cells = (0..self.width * height).map(|_i| Cell::Dead).collect();
    }

}
#}

We are going to create another impl Universe block inside our wasm_game_of_life/src/lib.rs file without the #[wasm_bindgen] attribute. There are a few functions we need for testing that we don't want to expose to our JavaScript. Rust-generated WebAssembly functions cannot return borrowed references. Try compiling the Rust-generated WebAssembly with the attribute and take a look at the errors you get.

We are going to write the implementation of get_cells to get the contents of the cells of a Universe. We'll also write a set_cells function so we can set cells in a specific row and column of a Universe to be Alive.

# #![allow(unused_variables)]
#fn main() {
impl Universe {
    /// Get the dead and alive values of the entire universe.
    pub fn get_cells(&self) -> &[Cell] {
        &self.cells
    }

    /// Set cells to be alive in a universe by passing the row and column
    /// of each cell as an array.
    pub fn set_cells(&mut self, cells: &[(u32, u32)]) {
        for (row, col) in cells.iter().cloned() {
            let idx = self.get_index(row, col);
            self.cells[idx] = Cell::Alive;
        }
    }

}
#}

Now we're going to create our test in the wasm_game_of_life/tests/web.rs file.

Before we do that, there is already one working test in the file. You can confirm that the Rust-generated WebAssembly test is working by running wasm-pack test --chrome --headless in the wasm-game-of-life directory. You can also use the --firefox, --safari, and --node options to test your code in those browsers.

In the wasm_game_of_life/tests/web.rs file, we need to export our wasm_game_of_life crate and the Universe type.

# #![allow(unused_variables)]
#fn main() {
extern crate wasm_game_of_life;
use wasm_game_of_life::Universe;
#}

In the wasm_game_of_life/tests/web.rs file we'll want to create some spaceship builder functions.

We'll want one for our input spaceship that we'll call the tick function on and we'll want the expected spaceship we will get after one tick. We picked the cells that we want to initialize as Alive to create our spaceship in the input_spaceship function. The position of the spaceship in the expected_spaceship function after the tick of the input_spaceship was calculated manually. You can confirm for yourself that the cells of the input spaceship after one tick is the same as the expected spaceship.

# #![allow(unused_variables)]
#fn main() {
#[cfg(test)]
pub fn input_spaceship() -> Universe {
    let mut universe = Universe::new();
    universe.set_width(6);
    universe.set_height(6);
    universe.set_cells(&[(1,2), (2,3), (3,1), (3,2), (3,3)]);
    universe
}

#[cfg(test)]
pub fn expected_spaceship() -> Universe {
    let mut universe = Universe::new();
    universe.set_width(6);
    universe.set_height(6);
    universe.set_cells(&[(2,1), (2,3), (3,2), (3,3), (4,2)]);
    universe
}
#}

Now we will write the implementation for our test_tick function. First, we create an instance of our input_spaceship() and our expected_spaceship(). Then, we call tick on the input_universe. Finally, we use the assert_eq! macro to call get_cells() to ensure that input_universe and expected_universe have the same Cell array values. We add the #[wasm_bindgen_test] attribute to our code block so we can test our Rust-generated WebAssembly code and use wasm-pack test to test the WebAssembly code.

# #![allow(unused_variables)]
#fn main() {
#[wasm_bindgen_test]
pub fn test_tick() {
    // Let's create a smaller Universe with a small spaceship to test!
    let mut input_universe = input_spaceship();

    // This is what our spaceship should look like
    // after one tick in our universe.
    let expected_universe = expected_spaceship();

    // Call `tick` and then see if the cells in the `Universe`s are the same.
    input_universe.tick();
    assert_eq!(&input_universe.get_cells(), &expected_universe.get_cells());
}
#}

Run the tests within the wasm-game-of-life directory by running wasm-pack test --firefox --headless.