it: Create the 'gui-test' crate

The 'gui-test' crate is intended to provide a test framework for process
isolated and remote test cases. Like how I intend to test winit.

Signed-off-by: John Nunley <dev@notgull.net>

Cargo.toml

@@ -264,6 +264,7 @@ name = "window"
 resolver = "2"
 members = [
     "dpi",
+    "it/gui-test",
     "run-wasm",
 ]
 

it/gui-test/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "gui-test"
+version = "0.1.0"
+rust-version.workspace = true
+repository.workspace = true
+license.workspace = true
+edition.workspace = true
+
+[dependencies]
+async-executor = "1.8.0"
+async-io = "2.3.1"
+async-lock = "3.3.0"
+async-process = "2.1.0"
+inventory = "0.3.15"
+serde = { workspace = true, features = ["derive"] }

it/gui-test/src/lib.rs

@@ -0,0 +1,391 @@
+//! A testing framework that can be run remotely.
+
+use serde::{Deserialize, Serialize};
+
+use std::env;
+use std::ffi::{OsStr, OsString};
+use std::mem;
+use std::num::NonZeroUsize;
+
+const GUI_TEST_CURRENT_TEST_NAME: &str = "GUI_TEST_CURRENT_TEST_NAME";
+const GUI_TEST_SUBPROCESS_LIMIT: &str = "GUI_TEST_SUBPROCESS_LIMIT";
+const DEFAULT_LIMIT: usize = 4;
+
+#[doc(hidden)]
+pub use inventory as __inventory;
+
+/// Replacement for the `main` function.
+#[macro_export]
+macro_rules! main {
+    ($harness:expr) => {
+        fn main() {
+            $crate::__entry($harness)
+        }
+    };
+}
+
+/// Set up a test for the test framework.
+#[macro_export]
+macro_rules! test {
+    (
+        $(#[$attr:meta])*
+        fn $name:ident ($hname:ident : $htype:ty) $bl:block
+    ) => {
+        const _: () = {
+            $(#[$attr])*
+            fn $name ($hname: $htype) $bl
+
+            $crate::__inventory::submit! {
+                $crate::__TestStart::__new(
+                    stringify!($name),
+                    $name
+                )
+            }
+        };
+    };
+}
+
+/// Test start.
+#[doc(hidden)]
+pub struct __TestStart {
+    /// The name of the test.
+    name: &'static str,
+
+    /// The function to call.
+    func: fn(&mut Harness),
+}
+
+impl __TestStart {
+    /// Create a new test start.
+    #[doc(hidden)]
+    pub fn __new(name: &'static str, func: fn(&mut Harness)) -> Self {
+        Self { name, func }
+    }
+}
+
+inventory::collect! {
+    __TestStart
+}
+
+/// A harness for running the tests.
+pub struct Harness {
+    /// Name of the test start.
+    name: String,
+
+    /// The inner test handler.
+    handler: Box<dyn TestHandler + Send + 'static>,
+
+    /// Number of tests that have been run so far.
+    test_count: usize,
+
+    /// Number of tests that have failed so far.
+    test_fails: usize,
+
+    /// Number of tests that have succeeded.
+    test_passed: usize,
+
+    /// Current state of the test harness.
+    state: State,
+}
+
+impl Harness {
+    /// Create a new test harness.
+    fn new<H: TestHandler + Send + 'static>(name: &str, handler: H) -> Self {
+        Self {
+            name: name.to_string(),
+            handler: Box::new(handler),
+            test_count: 0,
+            test_fails: 0,
+            test_passed: 0,
+            state: State::Default,
+        }
+    }
+
+    /// Begin a test.
+    pub fn test(&mut self, name: impl Into<String>) -> Testing<'_> {
+        // Make sure we aren't mid test.
+        match mem::replace(&mut self.state, State::Default) {
+            State::InTest { past_groups } => {
+                self.state = State::InTest { past_groups };
+                panic!("tried to start a test while another was underway");
+            }
+
+            State::InGroups(groups) => {
+                self.state = State::InTest {
+                    past_groups: Some(groups),
+                };
+            }
+
+            State::Default => {
+                self.state = State::InTest { past_groups: None };
+            }
+        }
+
+        // Send the "test started" event to the handler.
+        self.handler.handle_test(TestEvent {
+            runner: self.name.clone(),
+            ty: TestEventType::TestStarted { name: name.into() },
+        });
+
+        // Return the handle.
+        Testing {
+            harness: Some(self),
+        }
+    }
+
+    /// Run a closure as a test.
+    pub fn with_test<T>(&mut self, name: impl Into<String>, f: impl FnOnce() -> T) -> T {
+        let _test = self.test(name.into());
+        f()
+    }
+
+    /// Begin a test group.
+    pub fn group(&mut self, name: impl Into<String>) -> Grouping<'_> {
+        // Make sure we can begin a group.
+        match mem::replace(&mut self.state, State::Default) {
+            State::Default => {
+                self.state = State::InGroups(NonZeroUsize::new(1).unwrap());
+            }
+            State::InGroups(groups) => {
+                self.state = State::InGroups(groups.checked_add(1).unwrap());
+            }
+            State::InTest { past_groups } => {
+                self.state = State::InTest { past_groups };
+                panic!("cannot start group mid-test")
+            }
+        }
+
+        // Send the "group started" event to the handler.
+        self.handler.handle_test(TestEvent {
+            ty: TestEventType::GroupStarted { name: name.into() },
+            runner: self.name.clone(),
+        });
+
+        // Return the handle.
+        Grouping { harness: self }
+    }
+
+    /// Run a closure inside of a group.
+    pub fn with_group<T>(&mut self, name: impl Into<String>, f: impl FnOnce(&mut Self) -> T) -> T {
+        let mut group = self.group(name.into());
+        f(group.harness())
+    }
+
+    /// End an ongoing test.
+    fn end_test(&mut self, reason: TestResult) {
+        self.test_count += 1;
+        match &reason {
+            TestResult::Passed => self.test_passed += 1,
+            TestResult::Failed(..) => self.test_fails += 1,
+            _ => {}
+        }
+
+        self.handler.handle_test(TestEvent {
+            runner: self.name.clone(),
+            ty: TestEventType::TestEnded { result: reason },
+        });
+
+        let count = match mem::replace(&mut self.state, State::Default) {
+            State::InTest { past_groups } => past_groups,
+            _ => unreachable!(),
+        };
+
+        self.state = match count {
+            None => State::Default,
+            Some(count) => State::InGroups(count),
+        };
+    }
+
+    /// End the current group.
+    fn end_group(&mut self) {
+        self.handler.handle_test(TestEvent {
+            runner: self.name.clone(),
+            ty: TestEventType::GroupEnded,
+        });
+
+        let count = match mem::replace(&mut self.state, State::Default) {
+            State::InGroups(groups) => groups,
+            _ => unreachable!(),
+        };
+
+        self.state = match NonZeroUsize::new(count.get() - 1) {
+            None => State::Default,
+            Some(groups) => State::InGroups(groups),
+        };
+    }
+}
+
+/// An in-progress test.
+pub struct Testing<'a> {
+    harness: Option<&'a mut Harness>,
+}
+
+impl Testing<'_> {
+    /// Skip this test.
+    pub fn skip(mut self) {
+        // Send the "skipped" event.
+        self.harness.take().unwrap().end_test(TestResult::Skipped);
+    }
+}
+
+impl Drop for Testing<'_> {
+    fn drop(&mut self) {
+        if let Some(harness) = self.harness.take() {
+            let result = if std::thread::panicking() {
+                TestResult::Failed("thread panicked".into())
+            } else {
+                TestResult::Passed
+            };
+
+            harness.end_test(result);
+        }
+    }
+}
+
+/// We are running a test group.
+pub struct Grouping<'a> {
+    harness: &'a mut Harness,
+}
+
+impl Grouping<'_> {
+    /// Get the underlying test harness.
+    pub fn harness(&mut self) -> &mut Harness {
+        &mut self.harness
+    }
+}
+
+impl Drop for Grouping<'_> {
+    fn drop(&mut self) {
+        self.harness.end_group();
+    }
+}
+
+/// Current testing state.
+enum State {
+    /// We are in the middle of this many groups.
+    InGroups(NonZeroUsize),
+
+    /// We are in the middle of a test.
+    InTest { past_groups: Option<NonZeroUsize> },
+
+    /// We are in the default state.
+    Default,
+}
+
+/// A handler for incoming test events.
+pub trait TestHandler {
+    /// Handle a test.
+    fn handle_test(&mut self, event: TestEvent);
+}
+
+/// An event produced by the test harness.
+#[non_exhaustive]
+#[derive(Debug, Serialize, Deserialize)]
+pub struct TestEvent {
+    /// The name of the runner associated with the event.
+    runner: String,
+
+    /// The type of the event.
+    ty: TestEventType,
+}
+
+/// The type of the event.
+#[non_exhaustive]
+#[derive(Debug, Serialize, Deserialize)]
+pub enum TestEventType {
+    /// The tests are complete and the harness can be disconnected.
+    Complete,
+
+    /// A test has started.
+    TestStarted { name: String },
+
+    /// A test has completed.
+    TestEnded { result: TestResult },
+
+    /// A test group has started.
+    GroupStarted { name: String },
+
+    /// A test group has ended.
+    GroupEnded,
+}
+
+/// The result of a test.
+#[non_exhaustive]
+#[derive(Debug, Serialize, Deserialize)]
+pub enum TestResult {
+    /// The test passed.
+    Passed,
+
+    /// The test failed with the provided error.
+    Failed(String),
+
+    /// The test was skipped.
+    Skipped,
+}
+
+/// Entry point of the test.
+#[doc(hidden)]
+pub fn __entry<H: TestHandler + Send + 'static>(handler: H) {
+    // Look for the test name environment variable.
+    if let Some(test_name) = env::var(GUI_TEST_CURRENT_TEST_NAME)
+        .ok()
+        .filter(|test_name| !test_name.is_empty())
+    {
+        // Find the provided test.
+        let test_to_run = inventory::iter::<__TestStart>
+            .into_iter()
+            .find(|test| test.name == test_name)
+            .unwrap_or_else(|| panic!("unable to find test '{test_name}'"));
+
+        // Create a harness.
+        let mut harness = Harness::new(test_to_run.name, handler);
+
+        // Run the test.
+        (test_to_run.func)(&mut harness);
+    } else {
+        // Run a subprocess for every test.
+        let limit = env::var(GUI_TEST_SUBPROCESS_LIMIT)
+            .ok()
+            .and_then(|limit| limit.parse::<usize>().ok())
+            .unwrap_or(DEFAULT_LIMIT);
+        let process_name = env::args_os().next().unwrap();
+
+        let sema = async_lock::Semaphore::new(limit);
+        let ex = async_executor::Executor::new();
+
+        async_io::block_on(ex.run(async {
+            let mut tasks = vec![];
+
+            // Set up an environment variable for this.
+            for test in inventory::iter::<__TestStart> {
+                // Acquire a guard.
+                let guard = sema.acquire().await;
+
+                // Spawn a subprocess.
+                let mut process = async_process::Command::new(&process_name)
+                    .envs(env::vars_os().chain(Some({
+                        (path(&GUI_TEST_CURRENT_TEST_NAME), path(&test.name))
+                    })))
+                    .spawn()
+                    .expect("failed to spawn child process");
+
+                // Spawn a task to poll that subprocess.
+                let task = ex.spawn(async move {
+                    let _guard = guard;
+                    process.status().await.unwrap()
+                });
+
+                tasks.push(task);
+            }
+
+            // Finish all of the tasks.
+            for task in tasks {
+                task.await;
+            }
+        }));
+    }
+}
+
+fn path<A: AsRef<OsStr>>(s: &A) -> OsString {
+    s.as_ref().into()
+}