Add snapshot tests for all demos

crates/egui_demo_lib/src/demo/demo_app_windows.rs

@@ -377,3 +377,58 @@ fn file_menu_button(ui: &mut Ui) {
         }
     });
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::demo::demo_app_windows::Demos;
+    use egui::Vec2;
+    use egui_kittest::kittest::Queryable;
+    use egui_kittest::snapshot::try_image_snapshot;
+    use egui_kittest::wgpu::TestRenderer;
+    use egui_kittest::Harness;
+
+    #[test]
+    fn demos_should_match_snapshot() {
+        let demos = Demos::default();
+
+        let mut errors = Vec::new();
+
+        for mut demo in demos.demos {
+            let name = demo
+                .name()
+                .split_once(" ")
+                .map(|(_, name)| name)
+                .unwrap_or(demo.name());
+
+            let mut harness = Harness::new(|ctx| {
+                demo.show(ctx, &mut true);
+            });
+
+            // We need to run the app for multiple frames before all windows have the right size
+            harness.run();
+            harness.run();
+            harness.run();
+
+            let window = harness.node().children().next().unwrap();
+            // TODO: Windows should probably have a label?
+            //let window = harness.get_by_name(name);
+
+            let size = window.raw_bounds().expect("window bounds").size();
+            harness = harness.with_size(Vec2::new(size.width as f32, size.height as f32));
+
+            // We need to run the app for some more frames...
+            harness.run();
+            harness.run();
+
+            let image = TestRenderer::new().render(&harness);
+            let result = try_image_snapshot(image, &format!("{}", name));
+            if let Err(err) = result {
+                errors.push(err);
+            }
+        }
+
+        if !errors.is_empty() {
+            panic!("Errors: {:#?}", errors);
+        }
+    }
+}

crates/egui_kittest/src/lib.rs

@@ -6,6 +6,8 @@ mod utils;
 #[cfg(feature = "wgpu")]
 pub mod wgpu;
 
+pub use kittest;
+
 use crate::utils::egui_vec2;
 pub use accesskit_consumer;
 use egui::accesskit::NodeId;

crates/egui_kittest/src/snapshot.rs

@@ -1,11 +1,23 @@
-pub fn image_snapshot(current: image::RgbaImage, name: &str) {
+use std::path::{Path, PathBuf};
+
+#[derive(Debug)]
+pub struct SnapshotError {
+    pub diff: i32,
+    pub diff_path: PathBuf,
+}
+
+pub fn try_image_snapshot(current: image::RgbaImage, name: &str) -> Result<(), SnapshotError> {
     let current =
         dify_image::RgbaImage::from_raw(current.width(), current.height(), current.into_raw())
             .unwrap();
 
-    let path = format!("tests/snapshots/{name}.png");
-    let diff_path = format!("tests/snapshots/{name}.diff.png");
-    let current_path = format!("tests/snapshots/{name}.new.png");
+    let snapshots_path = Path::new("tests/snapshots");
+
+    let path = snapshots_path.join(format!("{name}.png"));
+    std::fs::create_dir_all(path.parent().unwrap()).ok();
+
+    let diff_path = snapshots_path.join(format!("{name}.diff.png"));
+    let current_path = snapshots_path.join(format!("{name}.new.png"));
 
     std::fs::create_dir_all("tests/snapshots").ok();
 
@@ -15,7 +27,7 @@ pub fn image_snapshot(current: image::RgbaImage, name: &str) {
         Ok(image) => image.to_rgba8(),
         Err(err) => {
             println!("Error opening image: {err}");
-            println!("Saving current image as {path}");
+            println!("Saving current image as {path:?}");
             current.save(&path).unwrap();
 
             current.clone()
@@ -29,12 +41,26 @@ pub fn image_snapshot(current: image::RgbaImage, name: &str) {
 
         if std::env::var("UPDATE_SNAPSHOTS").is_ok() {
             current.save(&path).unwrap();
-            println!("Updated snapshot: {path}");
+            println!("Updated snapshot: {path:?}");
         } else {
-            panic!("Image did not match snapshot. Diff: {diff}, {diff_path}");
+            return Err(SnapshotError { diff, diff_path });
         }
     } else {
         // Delete old diff if it exists
         std::fs::remove_file(diff_path).ok();
     }
+
+    Ok(())
+}
+
+pub fn image_snapshot(current: image::RgbaImage, name: &str) {
+    match try_image_snapshot(current, name) {
+        Ok(_) => {}
+        Err(err) => {
+            panic!(
+                "{name} failed. Image did not match snapshot. Diff: {}, {:?}",
+                err.diff, err.diff_path
+            );
+        }
+    }
 }