How to Test in Yew and What Testing Strategies and Tools Are Available?

Yew Testing Strategies and Practices

Testing Yew applications requires considering the WebAssembly environment and Rust testing frameworks. This article introduces comprehensive testing strategies.

Unit Testing

1. Component Unit Testing

rust
use yew::prelude::*;
use wasm_bindgen_test::*;

wasm_bindgen_test_configure!(run_in_browser);

#[function_component(SimpleComponent)]
fn simple_component() -> Html {
    let count = use_state(|| 0);
    
    let increment = {
        let count = count.clone();
        Callback::from(move |_| count.set(*count + 1))
    };

    html! {
        <div>
            <button onclick={increment}>{ "Increment" }</button>
            <span>{ *count }</span>
        </div>
    }
}

#[wasm_bindgen_test]
async fn test_simple_component() {
    let result = yew::ServerRenderer::<SimpleComponent>::render().await;
    assert!(result.contains("Increment"));
    assert!(result.contains("0"));
}

2. Hook Unit Testing

rust
use yew::prelude::*;
use yew_hooks::prelude::*;

#[wasm_bindgen_test]
async fn test_use_counter() {
    let result = yew::ServerRenderer::<CounterComponent>::render().await;
    assert!(result.contains("Counter: 0"));
}

#[function_component(CounterComponent)]
fn counter_component() -> Html {
    let (count, set_count) = use_counter(0);

    html! {
        <div>
            <p>{ format!("Counter: {}", count) }</p>
            <button onclick={Callback::from(move |_| set_count(*count + 1))}>
                { "Increment" }
            </button>
        </div>
    }
}

Integration Testing

1. Component Interaction Testing

rust
use yew::prelude::*;
use wasm_bindgen_test::*;

#[function_component(FormComponent)]
fn form_component() -> Html {
    let username = use_state(|| String::new());
    let submitted = use_state(|| false);

    let onsubmit = {
        let username = username.clone();
        let submitted = submitted.clone();
        Callback::from(move |e: SubmitEvent| {
            e.prevent_default();
            if !username.is_empty() {
                submitted.set(true);
            }
        })
    };

    let oninput = {
        let username = username.clone();
        Callback::from(move |e: InputEvent| {
            let input: HtmlInputElement = e.target_unchecked_into();
            username.set(input.value());
        })
    };

    html! {
        <form onsubmit={onsubmit}>
            <input 
                type="text"
                value={(*username).clone()}
                oninput={oninput}
                placeholder="Username"
            />
            <button type="submit">{ "Submit" }</button>
            { if *submitted {
                html! { <p>{ "Form submitted!" }</p> }
            } else {
                html! {}
            }}
        </form>
    }
}

#[wasm_bindgen_test]
async fn test_form_submission() {
    let result = yew::ServerRenderer::<FormComponent>::render().await;
    assert!(result.contains("Username"));
    assert!(result.contains("Submit"));
}

2. Async Component Testing

rust
use yew::prelude::*;
use wasm_bindgen_futures::spawn_local;

#[function_component(AsyncComponent)]
fn async_component() -> Html {
    let data = use_state(|| String::new());
    let loading = use_state(|| false);

    let fetch_data = {
        let data = data.clone();
        let loading = loading.clone();
        Callback::from(move |_| {
            loading.set(true);
            
            spawn_local(async move {
                gloo_timers::future::sleep(std::time::Duration::from_millis(100)).await;
                data.set("Async data loaded!".to_string());
                loading.set(false);
            });
        })
    };

    html! {
        <div>
            <button onclick={fetch_data} disabled={*loading}>
                { if *loading { "Loading..." } else { "Fetch Data" } }
            </button>
            <p>{ &*data }</p>
        </div>
    }
}

#[wasm_bindgen_test]
async fn test_async_component() {
    let result = yew::ServerRenderer::<AsyncComponent>::render().await;
    assert!(result.contains("Fetch Data"));
    assert!(result.contains("Loading..."));
}

End-to-End Testing

1. Using `yew-app` for E2E Testing

rust
use yew::prelude::*;
use wasm_bindgen_test::*;

#[function_component(App)]
fn app() -> Html {
    let count = use_state(|| 0);

    let increment = {
        let count = count.clone();
        Callback::from(move |_| count.set(*count + 1))
    };

    html! {
        <div id="app">
            <h1>{ "Counter App" }</h1>
            <button id="increment-btn" onclick={increment}>
                { "Increment" }
            </button>
            <p id="count-display">{ *count }</p>
        </div>
    }
}

#[wasm_bindgen_test]
async fn test_counter_increment() {
    // Render application
    yew::Renderer::<App>::with_root(
        gloo::utils::document().get_element_by_id("output").unwrap(),
    ).render();

    // Simulate click
    let button = gloo::utils::document()
        .get_element_by_id("increment-btn")
        .unwrap();
    
    let event = web_sys::MouseEvent::new("click").unwrap();
    button.dispatch_event(&event).unwrap();

    // Verify result
    let display = gloo::utils::document()
        .get_element_by_id("count-display")
        .unwrap();
    
    assert_eq!(display.text_content().unwrap(), "1");
}

Mock and Stub

1. Mock HTTP Requests

rust
use yew::prelude::*;
use gloo_net::http::Request;

#[function_component(ApiComponent)]
fn api_component() -> Html {
    let user = use_state(|| None::<String>);
    let loading = use_state(|| false);

    let fetch_user = {
        let user = user.clone();
        let loading = loading.clone();
        Callback::from(move |_| {
            loading.set(true);

            spawn_local(async move {
                match Request::get("/api/user").send().await {
                    Ok(response) => {
                        if response.ok() {
                            if let Ok(data) = response.text().await {
                                user.set(Some(data));
                            }
                        }
                    }
                    Err(_) => {}
                }
                loading.set(false);
            });
        })
    };

    html! {
        <div>
            <button onclick={fetch_user} disabled={*loading}>
                { if *loading { "Loading..." } else { "Fetch User" } }
            </button>
            { if let Some(ref u) = *user {
                html! { <p>{ u }</p> }
            } else {
                html! {}
            }}
        </div>
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use wasm_bindgen_test::*;

    #[wasm_bindgen_test]
    async fn test_api_component_with_mock() {
        // In tests, you can use mock servers
        // Simplified here to test component rendering
        let result = yew::ServerRenderer::<ApiComponent>::render().await;
        assert!(result.contains("Fetch User"));
    }
}

2. Mock WebSocket

rust
use yew::prelude::*;
use gloo_net::websocket::Message;

#[function_component(WebSocketComponent)]
fn websocket_component() -> Html {
    let messages = use_state(|| Vec::<String>::new());
    let connected = use_state(|| false);

    let connect = {
        let messages = messages.clone();
        let connected = connected.clone();
        Callback::from(move |_| {
            let ws = gloo_net::websocket::futures::WebSocket::open("ws://localhost:8080");
            
            if let Ok(ws) = ws {
                let onmessage = {
                    let messages = messages.clone();
                    Callback::from(move |msg: Message| {
                        if let Message::Text(text) = msg {
                            let mut msgs = (*messages).clone();
                            msgs.push(text);
                            messages.set(msgs);
                        }
                    })
                };
                
                ws.set_onmessage(onmessage);
                connected.set(true);
            }
        })
    };

    html! {
        <div>
            <button onclick={connect} disabled={*connected}>
                { if *connected { "Connected" } else { "Connect" } }
            </button>
            <ul>
                { messages.iter().map(|msg| {
                    html! {
                        <li>{ msg }</li>
                    }
                }).collect::<Html>() }
            </ul>
        </div>
    }
}

Test Coverage

1. Using `tarpaulin` for Test Coverage

bash
# Install tarpaulin
cargo install cargo-tarpaulin

# Run coverage tests
cargo tarpaulin --out Html --output-dir ./coverage

# For Wasm tests
wasm-pack test --firefox --headless

2. Configure Test Coverage

toml
# Cargo.toml
[package]
name = "yew-app"
version = "0.1.0"
edition = "2021"

[dev-dependencies]
wasm-bindgen-test = "0.3"
gloo = "0.8"
web-sys = { version = "0.3", features = ["console"] }

Performance Testing

1. Component Rendering Performance Testing

rust
use yew::prelude::*;
use web_sys::Performance;

#[function_component(PerformanceTestComponent)]
fn performance_test_component() -> Html {
    let render_time = use_state(|| 0.0);

    let measure_render = {
        let render_time = render_time.clone();
        Callback::from(move |_| {
            if let Ok(performance) = Performance::new() {
                let start = performance.now();
                
                // Simulate render operation
                let _ = std::hint::black_box(42);
                
                let end = performance.now();
                render_time.set(end - start);
            }
        })
    };

    html! {
        <div>
            <button onclick={measure_render}>{ "Measure Render" }</button>
            <p>{ "Render time: " }{ *render_time }{ " ms" }</p>
        </div>
    }
}

#[wasm_bindgen_test]
async fn test_render_performance() {
    let result = yew::ServerRenderer::<PerformanceTestComponent>::render().await;
    assert!(result.contains("Measure Render"));
    assert!(result.contains("Render time:"));
}

Testing Best Practices

1. Test Organization

rust
// tests/common/mod.rs
pub mod common {
    use yew::prelude::*;

    pub fn setup_test_environment() {
        // Setup test environment
    }

    pub fn cleanup_test_environment() {
        // Cleanup test environment
    }
}

// tests/components/button_test.rs
mod button_test {
    use super::common::*;
    use wasm_bindgen_test::*;

    #[wasm_bindgen_test]
    async fn test_button_render() {
        setup_test_environment();
        
        let result = yew::ServerRenderer::<ButtonComponent>::render().await;
        assert!(result.contains("Click me"));
        
        cleanup_test_environment();
    }
}

2. Test Data Management

rust
// tests/fixtures/mod.rs
pub mod fixtures {
    pub fn get_test_user() -> User {
        User {
            id: 1,
            name: "Test User".to_string(),
            email: "test@example.com".to_string(),
        }
    }

    pub fn get_test_posts() -> Vec<Post> {
        vec![
            Post {
                id: 1,
                title: "Test Post 1".to_string(),
                body: "Test content".to_string(),
            },
            Post {
                id: 2,
                title: "Test Post 2".to_string(),
                body: "More test content".to_string(),
            },
        ]
    }
}

Continuous Integration

1. GitHub Actions Configuration

yaml
# .github/workflows/test.yml
name: Test

on:
  push:
    branches: [ main ]
  pull_request:
    branches: [ main ]

jobs:
  test:
    runs-on: ubuntu-latest
    
    steps:
    - uses: actions/checkout@v2
    
    - name: Install Rust
      uses: actions-rs/toolchain@v1
      with:
        toolchain: stable
        override: true
    
    - name: Install wasm-pack
      run: curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh
    
    - name: Run tests
      run: |
        cargo test --all
        wasm-pack test --firefox --headless
    
    - name: Run coverage
      run: cargo tarpaulin --out Xml

2. GitLab CI Configuration

yaml
# .gitlab-ci.yml
stages:
  - test

test:
  stage: test
  image: rust:latest
  
  before_script:
    - curl https://rustwasm.github.io/wasm-pack/installer/init.sh -sSf | sh
  
  script:
    - cargo test --all
    - wasm-pack test --firefox --headless
    - cargo tarpaulin --out Xml
  
  coverage: '/^\d+.\d+% coverage/'
  artifacts:
    reports:
      coverage_report:
        coverage_format: cobertura
        path: cobertura.xml

Debugging Tests

1. Using Browser Developer Tools

rust
use web_sys::console;

#[wasm_bindgen_test]
async fn test_with_debugging() {
    console::log_1(&"Starting test".into());
    
    let result = yew::ServerRenderer::<TestComponent>::render().await;
    
    console::log_2(
        &"Render result:".into(),
        &result.into()
    );
    
    assert!(result.contains("Expected content"));
}

2. Using `console_error_panic_hook`

rust
use console_error_panic_hook;

#[wasm_bindgen_test]
async fn test_with_panic_hook() {
    console_error_panic_hook::set_once();
    
    // Test code
    let result = yew::ServerRenderer::<TestComponent>::render().await;
    assert!(result.contains("Expected content"));
}

Recommended Testing Tools

wasm-bindgen-test: Wasm environment testing framework
yew-app: Yew application testing tool
gloo: Web API bindings and utilities
cargo-tarpaulin: Code coverage tool
web-sys: Web API bindings

Summary

Yew testing requires combining Rust testing frameworks with WebAssembly characteristics. Through reasonable testing strategies, mock techniques, and continuous integration configuration, you can build high-quality Yew applications.