diff --git a/crates/ui-egui/src/prefs_dialog.rs b/crates/ui-egui/src/prefs_dialog.rs
index 9057aeb13..79121f85d 100644
--- a/crates/ui-egui/src/prefs_dialog.rs
+++ b/crates/ui-egui/src/prefs_dialog.rs
@@ -418,380 +418,4 @@ fn labeled(ui: &mut egui::Ui, label: &str, add: impl FnOnce(&mut egui::Ui)) {
 }
 
 #[cfg(test)]
-mod tests {
-    use super::*;
-    use crate::Services;
-    use vectorcraft_engine::Session;
-
-    #[test]
-    fn geometric_snapping_is_a_saved_smart_guides_preference() {
-        let mut a = VectorcraftApp::new(vectorcraft_engine::Session::new(), Default::default());
-        open(&mut a, Some("Smart Guides"));
-        let text = crate::tests_labels::painted_text(&mut a, |a, ui| show(a, ui.ctx()));
-        assert!(text.contains("Geometric Guides") && text.contains("Snap to Perpendicular") && text.contains("Snap to Tangent"), "{text}");
-        a.ui.dialog.as_mut().unwrap().fields.insert("snapPerpendicular".into(), json!(false));
-        confirm(&mut a).unwrap();
-        assert!(!a.session.prefs.snap_perpendicular && a.session.prefs.snap_tangent);
-        let saved: Prefs = serde_json::from_value(a.ui.engine_prefs.clone()).unwrap();
-        assert!(!saved.snap_perpendicular && saved.snap_tangent);
-        assert!(a.run("view.snapping", json!({})).is_err());
-    }
-
-    /// A resting checkbox must have a visible outline in both states and every brightness.
-    #[test]
-    fn preference_checkboxes_draw_outlines_without_hover() {
-        for brightness in Brightness::ALL {
-            let ctx = egui::Context::default();
-            crate::theme::install_fonts(&ctx);
-            theme::apply(&ctx, brightness);
-            for checked in [false, true] {
-                let mut d = Dialog::new("preferences", json!({"showToolTips": checked}));
-                let raw =
-                    egui::RawInput { screen_rect: Some(egui::Rect::from_min_size(egui::Pos2::ZERO, egui::vec2(400.0, 200.0))), ..Default::default() };
-                let mut out = ctx.run_ui(raw, |ui| bool_row(ui, &mut d, "showToolTips", "Show Tool Tips"));
-                out.textures_delta.clear();
-                let outlined = out.shapes.iter().any(|shape| match &shape.shape {
-                    egui::Shape::Rect(r) => r.stroke.width > 0.0 && r.rect.width() <= 24.0 && r.rect.height() <= 24.0,
-                    _ => false,
-                });
-                assert!(outlined, "{brightness:?}, checked={checked}: no checkbox outline");
-            }
-        }
-    }
-
-    /// User Interface › Canvas Color (#663): White and the three greys paint the canvas around the
-    /// artboards; Match User Interface Brightness keeps the theme's.
-    #[test]
-    fn canvas_color_choices_paint_the_pasteboard() {
-        let mut app = VectorcraftApp::new(Session::new(), Services::default());
-        let ctx = egui::Context::default();
-        apply_runtime(&mut app, &ctx);
-        let themed = Tokens::get(&ctx).pasteboard;
-        for (key, want) in [
-            ("white", egui::Color32::WHITE),
-            ("lightGray", egui::Color32::from_gray(0xc8)),
-            ("mediumGray", egui::Color32::from_gray(0x96)),
-            ("darkGray", egui::Color32::from_gray(0x5a)),
-            ("matchUi", themed),
-        ] {
-            app.run("prefs.set", serde_json::json!({"key": "canvasColor", "value": key})).unwrap();
-            apply_runtime(&mut app, &ctx);
-            assert_eq!(Tokens::get(&ctx).pasteboard, want, "{key}");
-        }
-        assert!(app.run("prefs.set", serde_json::json!({"key": "canvasColor", "value": "pink"})).is_err());
-    }
-
-    fn app() -> VectorcraftApp {
-        VectorcraftApp::new(Session::new(), Services::default())
-    }
-
-    #[test]
-    fn dialog_ok_applies_prefs_and_ui_fields() {
-        let mut a = app();
-        open(&mut a, Some("general"));
-        let d = a.ui.dialog.as_mut().unwrap();
-        assert_eq!(d.str("__category"), "General");
-        d.fields.insert("keyboardIncrement".into(), json!(4));
-        d.fields.insert("uiBrightness".into(), json!("light"));
-        d.fields.insert("__smartGuides".into(), json!(false));
-        confirm(&mut a).unwrap();
-        assert!(a.ui.dialog.is_none());
-        assert_eq!(a.session.prefs.keyboard_increment, 4.0);
-        assert_eq!(a.session.prefs.ui_brightness, "light");
-        assert!(!a.ui.view.smart_guides);
-        assert_eq!(a.ui.engine_prefs["keyboardIncrement"], json!(4.0));
-    }
-
-    /// General › Show Tool Tips: off, a button held under the pointer shows no tool tip; back on,
-    /// it does again (#394).
-    #[test]
-    fn show_tool_tips_off_hides_tool_tips() {
-        fn texts(s: &egui::Shape, out: &mut Vec<String>) {
-            match s {
-                egui::Shape::Text(t) => out.push(t.galley.text().to_string()),
-                egui::Shape::Vec(v) => v.iter().for_each(|s| texts(s, out)),
-                _ => {}
-            }
-        }
-        let mut a = app();
-        let ctx = egui::Context::default();
-        let mut time = 0.0;
-        // Come from elsewhere and hover the button for two seconds: did its tool tip show?
-        let mut hover = |a: &mut VectorcraftApp| {
-            let mut shown = vec![];
-            for i in 0..20 {
-                time += 0.1;
-                let events = match i {
-                    0 => vec![egui::Event::PointerGone],
-                    1 => vec![egui::Event::PointerMoved(egui::pos2(20.0, 12.0))],
-                    _ => vec![],
-                };
-                let raw = egui::RawInput {
-                    events,
-                    time: Some(time),
-                    screen_rect: Some(egui::Rect::from_min_size(egui::Pos2::ZERO, egui::vec2(400.0, 300.0))),
-                    ..Default::default()
-                };
-                let mut out = ctx.run_ui(raw, |ui| {
-                    apply_runtime(a, ui.ctx());
-                    ui.button("Button").on_hover_text("The tool tip");
-                });
-                out.textures_delta.clear();
-                out.shapes.iter().for_each(|c| texts(&c.shape, &mut shown));
-            }
-            shown.iter().any(|t| t == "The tool tip")
-        };
-        assert!(hover(&mut a), "on by default");
-        a.run("prefs.set", json!({"key": "showToolTips", "value": false})).unwrap();
-        assert!(!hover(&mut a), "off: no tool tip");
-        a.run("prefs.set", json!({"key": "showToolTips", "value": true})).unwrap();
-        assert!(hover(&mut a), "on again");
-    }
-
-    #[test]
-    fn dialog_ok_with_invalid_value_keeps_dialog_and_prefs() {
-        let mut a = app();
-        open(&mut a, None);
-        a.ui.dialog.as_mut().unwrap().fields.insert("anchorSize".into(), json!(42));
-        assert!(confirm(&mut a).is_err());
-        assert!(a.ui.dialog.is_some());
-        assert_eq!(a.session.prefs, Prefs::default());
-    }
-
-    #[test]
-    fn prefs_persist_through_ui_state() {
-        let mut a = app();
-        a.run("prefs.set", json!({"key": "gridlineEvery", "value": 50})).unwrap();
-        snapshot(&mut a);
-        let saved = serde_json::to_vec(&a.ui).unwrap();
-        let mut b = app();
-        b.ui = serde_json::from_slice::<crate::UiState>(&saved).unwrap().sanitized();
-        restore(&mut b);
-        assert_eq!(b.session.prefs.gridline_every, 50.0);
-    }
-
-    #[test]
-    fn old_pref_files_keep_their_brightness() {
-        let mut a = app();
-        a.ui.brightness = Brightness::Light;
-        a.ui.engine_prefs = Value::Null;
-        restore(&mut a);
-        assert_eq!(a.session.prefs.ui_brightness, "light");
-    }
-
-    /// Performance › Graphics Processor (#306, #502): shown with its restart note, applied by OK
-    /// and saved with the UI state under the key the desktop app reads before the window opens.
-    #[test]
-    fn graphics_processor_preference_shows_and_persists() {
-        fn texts(s: &egui::Shape, out: &mut Vec<String>) {
-            match s {
-                egui::Shape::Text(t) => out.push(t.galley.text().to_string()),
-                egui::Shape::Vec(v) => v.iter().for_each(|s| texts(s, out)),
-                _ => {}
-            }
-        }
-        let mut a = app();
-        open(&mut a, Some("Performance"));
-        let ctx = egui::Context::default();
-        crate::theme::install_fonts(&ctx);
-        // The window sizes itself on the first frame and draws on the second.
-        let mut out = ctx.run_ui(egui::RawInput::default(), |ui| show(&mut a, ui.ctx()));
-        out.textures_delta.clear();
-        let mut out = ctx.run_ui(egui::RawInput::default(), |ui| show(&mut a, ui.ctx()));
-        out.textures_delta.clear();
-        let mut shown = vec![];
-        out.shapes.iter().for_each(|c| texts(&c.shape, &mut shown));
-        assert!(shown.iter().any(|t| t.starts_with("Graphics Processor")), "{shown:?}");
-        assert!(shown.iter().any(|t| t == "Automatic"), "{shown:?}");
-        assert!(shown.iter().any(|t| t == "Applies the next time VectorCraft starts."), "{shown:?}");
-        a.ui.dialog.as_mut().unwrap().fields.insert("gpuPreference".into(), json!("highPerformance"));
-        assert!(!a.take_prefs_changed(), "nothing to write before OK");
-        confirm(&mut a).unwrap();
-        assert!(a.take_prefs_changed(), "OK asks the host to write the preferences file");
-        assert!(!a.take_prefs_changed());
-        assert_eq!(a.session.prefs.gpu_preference, "highPerformance");
-        let saved: Value = serde_json::from_slice(&serde_json::to_vec(&a.ui).unwrap()).unwrap();
-        assert_eq!(saved["engine_prefs"]["gpuPreference"], json!("highPerformance"));
-    }
-
-    /// User Interface › System Title Bar: shown with its next-launch note, applied by OK and
-    /// saved with the UI state under the key the desktop app reads before the window opens.
-    #[test]
-    fn system_title_bar_preference_shows_and_persists() {
-        fn texts(s: &egui::Shape, out: &mut Vec<String>) {
-            match s {
-                egui::Shape::Text(t) => out.push(t.galley.text().to_string()),
-                egui::Shape::Vec(v) => v.iter().for_each(|s| texts(s, out)),
-                _ => {}
-            }
-        }
-        let mut a = app();
-        open(&mut a, Some("User Interface"));
-        let ctx = egui::Context::default();
-        crate::theme::install_fonts(&ctx);
-        // The window sizes itself on the first frame and draws on the second.
-        let mut out = ctx.run_ui(egui::RawInput::default(), |ui| show(&mut a, ui.ctx()));
-        out.textures_delta.clear();
-        let mut out = ctx.run_ui(egui::RawInput::default(), |ui| show(&mut a, ui.ctx()));
-        out.textures_delta.clear();
-        let mut shown = vec![];
-        out.shapes.iter().for_each(|c| texts(&c.shape, &mut shown));
-        let supported = cfg!(all(not(target_arch = "wasm32"), not(target_os = "macos")));
-        assert_eq!(shown.iter().any(|t| t == "System Title Bar"), supported, "{shown:?}");
-        assert_eq!(shown.iter().any(|t| t == "Applies the next time VectorCraft starts."), supported, "{shown:?}");
-        a.ui.dialog.as_mut().unwrap().fields.insert("systemTitleBar".into(), json!(true));
-        confirm(&mut a).unwrap();
-        assert!(a.session.prefs.system_title_bar);
-        let saved: Value = serde_json::from_slice(&serde_json::to_vec(&a.ui).unwrap()).unwrap();
-        assert_eq!(saved["engine_prefs"]["systemTitleBar"], json!(true));
-    }
-
-    /// Performance › Linux Display Server (#2028): on Linux it shows the drawing-tablet note, and
-    /// X11 (XWayland) When a Pen Is Attached is applied by OK and saved under the key the desktop
-    /// app reads before the window opens.
-    #[test]
-    fn linux_display_server_offers_the_pen_choice() {
-        fn texts(s: &egui::Shape, out: &mut Vec<String>) {
-            match s {
-                egui::Shape::Text(t) => out.push(t.galley.text().to_string()),
-                egui::Shape::Vec(v) => v.iter().for_each(|s| texts(s, out)),
-                _ => {}
-            }
-        }
-        let mut a = app();
-        open(&mut a, Some("Performance"));
-        let ctx = egui::Context::default();
-        crate::theme::install_fonts(&ctx);
-        // The window sizes itself on the first frame and draws on the second.
-        let mut out = ctx.run_ui(egui::RawInput::default(), |ui| show(&mut a, ui.ctx()));
-        out.textures_delta.clear();
-        let mut out = ctx.run_ui(egui::RawInput::default(), |ui| show(&mut a, ui.ctx()));
-        out.textures_delta.clear();
-        let mut shown = vec![];
-        out.shapes.iter().for_each(|c| texts(&c.shape, &mut shown));
-        let linux = cfg!(target_os = "linux");
-        assert_eq!(shown.iter().any(|t| t.starts_with("Linux Display Server")), linux, "{shown:?}");
-        let note = "If a drawing tablet's pen doesn't draw, choose an X11 (XWayland) option.";
-        assert_eq!(shown.iter().any(|t| t == note), linux, "{shown:?}");
-        a.ui.dialog.as_mut().unwrap().fields.insert("linuxDisplayServer".into(), json!("x11WithPen"));
-        confirm(&mut a).unwrap();
-        assert_eq!(a.session.prefs.linux_display_server, "x11WithPen");
-        let saved: Value = serde_json::from_slice(&serde_json::to_vec(&a.ui).unwrap()).unwrap();
-        assert_eq!(saved["engine_prefs"]["linuxDisplayServer"], json!("x11WithPen"));
-    }
-
-    /// #1866: the category shown is highlighted in the list while the pointer is elsewhere.
-    #[test]
-    fn the_category_shown_is_highlighted() {
-        fn rects(s: &egui::Shape, out: &mut Vec<(egui::Rect, egui::Color32)>) {
-            match s {
-                egui::Shape::Rect(r) => out.push((r.rect, r.fill)),
-                egui::Shape::Vec(v) => v.iter().for_each(|s| rects(s, out)),
-                _ => {}
-            }
-        }
-        let mut a = app();
-        open(&mut a, Some("Units"));
-        let ctx = egui::Context::default();
-        crate::theme::install_fonts(&ctx);
-        // The window sizes itself on the first frame and draws on the second.
-        let mut out = ctx.run_ui(egui::RawInput::default(), |ui| show(&mut a, ui.ctx()));
-        out.textures_delta.clear();
-        let mut out = ctx.run_ui(egui::RawInput::default(), |ui| show(&mut a, ui.ctx()));
-        out.textures_delta.clear();
-        let mut shown = vec![];
-        out.shapes.iter().for_each(|c| rects(&c.shape, &mut shown));
-        // The list's rows, top to bottom: only the fourth (Units) is filled.
-        let rows: Vec<_> = shown.iter().filter(|(r, _)| r.width() == 184.0 && r.height() < 30.0).collect();
-        assert_eq!(rows.len(), PREF_CATEGORIES.len(), "{shown:?}");
-        let filled: Vec<usize> = rows.iter().enumerate().filter(|(_, (_, c))| c.a() > 0).map(|(i, _)| i).collect();
-        assert_eq!(filled, vec![3], "{rows:?}");
-    }
-
-    /// Units › Numbers Without Units Are Points (#394): the preference reaches the fields when it
-    /// changes, and its checkbox is dimmed unless a unit is Picas.
-    #[test]
-    fn numbers_without_units_are_points_reaches_the_fields_and_dims_without_picas() {
-        let mut a = app();
-        let ctx = egui::Context::default();
-        crate::theme::install_fonts(&ctx);
-        let frame = |a: &mut VectorcraftApp| {
-            let mut out = ctx.run_ui(egui::RawInput::default(), |ui| {
-                apply_runtime(a, ui.ctx());
-                show(a, ui.ctx());
-            });
-            out.textures_delta.clear();
-        };
-        let read = |ctx: &egui::Context| widgets::typed_unit(ctx, vectorcraft_doc::Unit::Picas);
-        frame(&mut a);
-        assert_eq!(read(&ctx), vectorcraft_doc::Unit::Points, "on by default");
-        a.run("prefs.set", json!({"key": "numbersWithoutUnitsArePoints", "value": false})).unwrap();
-        frame(&mut a);
-        assert_eq!(read(&ctx), vectorcraft_doc::Unit::Picas, "off");
-        // The checkbox: dimmed with every unit in points, enabled once a unit is Picas.
-        open(&mut a, Some("Units"));
-        let d = a.ui.dialog.as_mut().unwrap();
-        assert!(!picas_in_use(d), "dimmed in points");
-        d.fields.insert("unitsStroke".into(), json!("picas"));
-        assert!(picas_in_use(d), "enabled with a unit in picas");
-    }
-
-    /// 0.5.0 saved `powerSaving` for everyone (its default): it reads as Automatic, while the
-    /// choices this version offers are kept (#502).
-    #[test]
-    fn a_graphics_processor_this_version_does_not_offer_reads_as_automatic() {
-        for (saved, read) in [("powerSaving", "automatic"), ("turbo", "automatic"), ("lowPower", "lowPower"), ("highPerformance", "highPerformance")]
-        {
-            let mut a = app();
-            a.ui.engine_prefs = json!({"gpuPreference": saved});
-            restore(&mut a);
-            assert_eq!(a.session.prefs.gpu_preference, read, "{saved}");
-        }
-    }
-
-    #[test]
-    fn every_category_renders_fields() {
-        for c in PREF_CATEGORIES {
-            assert!(PREF_SPECS.iter().any(|s| s.category == *c));
-        }
-    }
-
-    /// Preferences › Type › Show Font Names in English (#394): OK on the dialog stores the flag the
-    /// font menus read (Character panel, Type → Font).
-    #[test]
-    fn show_font_names_in_english_dialog_ok_stores_the_flag() {
-        let mut a = app();
-        assert!(a.session.prefs.font_names_in_english);
-        open(&mut a, Some("Type"));
-        assert_eq!(a.ui.dialog.as_ref().unwrap().str("__category"), "Type");
-        a.ui.dialog.as_mut().unwrap().fields.insert("fontNamesInEnglish".into(), json!(false));
-        confirm(&mut a).unwrap();
-        assert!(a.ui.dialog.is_none());
-        assert!(!a.session.prefs.font_names_in_english);
-        assert!(!crate::font_menu::MenuLook::of(&a).english_names);
-    }
-
-    /// Preferences › Hyphenation › Exceptions (#394): OK on the dialog pushes the list into the
-    /// hyphenator the same way `prefs.set` does (no need to drive the live Preferences window).
-    #[test]
-    fn hyphenation_exceptions_dialog_ok_reaches_the_hyphenator() {
-        struct Clear;
-        impl Drop for Clear {
-            fn drop(&mut self) {
-                vectorcraft_text::set_hyphenation_exceptions("");
-            }
-        }
-        let _clear = Clear;
-        let mut a = app();
-        open(&mut a, Some("Hyphenation"));
-        let d = a.ui.dialog.as_mut().unwrap();
-        assert_eq!(d.str("__category"), "Hyphenation");
-        d.fields.insert("hyphenationExceptions".into(), json!("typography, hap-pen"));
-        confirm(&mut a).unwrap();
-        assert!(a.ui.dialog.is_none());
-        assert_eq!(a.session.prefs.hyphenation_exceptions, "typography, hap-pen");
-        assert_eq!(vectorcraft_text::hyphenation_exceptions(), "typography, hap-pen");
-        assert!(vectorcraft_text::hyphen::hyphen_points("typography").is_empty());
-        assert_eq!(vectorcraft_text::hyphen::hyphen_points("happen"), vec![3]);
-    }
-}
+mod tests;
diff --git a/crates/ui-egui/src/prefs_dialog/tests.rs b/crates/ui-egui/src/prefs_dialog/tests.rs
new file mode 100644
index 000000000..dd8617977
--- /dev/null
+++ b/crates/ui-egui/src/prefs_dialog/tests.rs
@@ -0,0 +1,375 @@
+use super::*;
+use crate::Services;
+use vectorcraft_engine::Session;
+
+#[test]
+fn geometric_snapping_is_a_saved_smart_guides_preference() {
+    let mut a = VectorcraftApp::new(vectorcraft_engine::Session::new(), Default::default());
+    open(&mut a, Some("Smart Guides"));
+    let text = crate::tests_labels::painted_text(&mut a, |a, ui| show(a, ui.ctx()));
+    assert!(text.contains("Geometric Guides") && text.contains("Snap to Perpendicular") && text.contains("Snap to Tangent"), "{text}");
+    a.ui.dialog.as_mut().unwrap().fields.insert("snapPerpendicular".into(), json!(false));
+    confirm(&mut a).unwrap();
+    assert!(!a.session.prefs.snap_perpendicular && a.session.prefs.snap_tangent);
+    let saved: Prefs = serde_json::from_value(a.ui.engine_prefs.clone()).unwrap();
+    assert!(!saved.snap_perpendicular && saved.snap_tangent);
+    assert!(a.run("view.snapping", json!({})).is_err());
+}
+
+/// A resting checkbox must have a visible outline in both states and every brightness.
+#[test]
+fn preference_checkboxes_draw_outlines_without_hover() {
+    for brightness in Brightness::ALL {
+        let ctx = egui::Context::default();
+        crate::theme::install_fonts(&ctx);
+        theme::apply(&ctx, brightness);
+        for checked in [false, true] {
+            let mut d = Dialog::new("preferences", json!({"showToolTips": checked}));
+            let raw =
+                egui::RawInput { screen_rect: Some(egui::Rect::from_min_size(egui::Pos2::ZERO, egui::vec2(400.0, 200.0))), ..Default::default() };
+            let mut out = ctx.run_ui(raw, |ui| bool_row(ui, &mut d, "showToolTips", "Show Tool Tips"));
+            out.textures_delta.clear();
+            let outlined = out.shapes.iter().any(|shape| match &shape.shape {
+                egui::Shape::Rect(r) => r.stroke.width > 0.0 && r.rect.width() <= 24.0 && r.rect.height() <= 24.0,
+                _ => false,
+            });
+            assert!(outlined, "{brightness:?}, checked={checked}: no checkbox outline");
+        }
+    }
+}
+
+/// User Interface › Canvas Color (#663): White and the three greys paint the canvas around the
+/// artboards; Match User Interface Brightness keeps the theme's.
+#[test]
+fn canvas_color_choices_paint_the_pasteboard() {
+    let mut app = VectorcraftApp::new(Session::new(), Services::default());
+    let ctx = egui::Context::default();
+    apply_runtime(&mut app, &ctx);
+    let themed = Tokens::get(&ctx).pasteboard;
+    for (key, want) in [
+        ("white", egui::Color32::WHITE),
+        ("lightGray", egui::Color32::from_gray(0xc8)),
+        ("mediumGray", egui::Color32::from_gray(0x96)),
+        ("darkGray", egui::Color32::from_gray(0x5a)),
+        ("matchUi", themed),
+    ] {
+        app.run("prefs.set", serde_json::json!({"key": "canvasColor", "value": key})).unwrap();
+        apply_runtime(&mut app, &ctx);
+        assert_eq!(Tokens::get(&ctx).pasteboard, want, "{key}");
+    }
+    assert!(app.run("prefs.set", serde_json::json!({"key": "canvasColor", "value": "pink"})).is_err());
+}
+
+fn app() -> VectorcraftApp {
+    VectorcraftApp::new(Session::new(), Services::default())
+}
+
+#[test]
+fn dialog_ok_applies_prefs_and_ui_fields() {
+    let mut a = app();
+    open(&mut a, Some("general"));
+    let d = a.ui.dialog.as_mut().unwrap();
+    assert_eq!(d.str("__category"), "General");
+    d.fields.insert("keyboardIncrement".into(), json!(4));
+    d.fields.insert("uiBrightness".into(), json!("light"));
+    d.fields.insert("__smartGuides".into(), json!(false));
+    confirm(&mut a).unwrap();
+    assert!(a.ui.dialog.is_none());
+    assert_eq!(a.session.prefs.keyboard_increment, 4.0);
+    assert_eq!(a.session.prefs.ui_brightness, "light");
+    assert!(!a.ui.view.smart_guides);
+    assert_eq!(a.ui.engine_prefs["keyboardIncrement"], json!(4.0));
+}
+
+/// General › Show Tool Tips: off, a button held under the pointer shows no tool tip; back on,
+/// it does again (#394).
+#[test]
+fn show_tool_tips_off_hides_tool_tips() {
+    fn texts(s: &egui::Shape, out: &mut Vec<String>) {
+        match s {
+            egui::Shape::Text(t) => out.push(t.galley.text().to_string()),
+            egui::Shape::Vec(v) => v.iter().for_each(|s| texts(s, out)),
+            _ => {}
+        }
+    }
+    let mut a = app();
+    let ctx = egui::Context::default();
+    let mut time = 0.0;
+    // Come from elsewhere and hover the button for two seconds: did its tool tip show?
+    let mut hover = |a: &mut VectorcraftApp| {
+        let mut shown = vec![];
+        for i in 0..20 {
+            time += 0.1;
+            let events = match i {
+                0 => vec![egui::Event::PointerGone],
+                1 => vec![egui::Event::PointerMoved(egui::pos2(20.0, 12.0))],
+                _ => vec![],
+            };
+            let raw = egui::RawInput {
+                events,
+                time: Some(time),
+                screen_rect: Some(egui::Rect::from_min_size(egui::Pos2::ZERO, egui::vec2(400.0, 300.0))),
+                ..Default::default()
+            };
+            let mut out = ctx.run_ui(raw, |ui| {
+                apply_runtime(a, ui.ctx());
+                ui.button("Button").on_hover_text("The tool tip");
+            });
+            out.textures_delta.clear();
+            out.shapes.iter().for_each(|c| texts(&c.shape, &mut shown));
+        }
+        shown.iter().any(|t| t == "The tool tip")
+    };
+    assert!(hover(&mut a), "on by default");
+    a.run("prefs.set", json!({"key": "showToolTips", "value": false})).unwrap();
+    assert!(!hover(&mut a), "off: no tool tip");
+    a.run("prefs.set", json!({"key": "showToolTips", "value": true})).unwrap();
+    assert!(hover(&mut a), "on again");
+}
+
+#[test]
+fn dialog_ok_with_invalid_value_keeps_dialog_and_prefs() {
+    let mut a = app();
+    open(&mut a, None);
+    a.ui.dialog.as_mut().unwrap().fields.insert("anchorSize".into(), json!(42));
+    assert!(confirm(&mut a).is_err());
+    assert!(a.ui.dialog.is_some());
+    assert_eq!(a.session.prefs, Prefs::default());
+}
+
+#[test]
+fn prefs_persist_through_ui_state() {
+    let mut a = app();
+    a.run("prefs.set", json!({"key": "gridlineEvery", "value": 50})).unwrap();
+    snapshot(&mut a);
+    let saved = serde_json::to_vec(&a.ui).unwrap();
+    let mut b = app();
+    b.ui = serde_json::from_slice::<crate::UiState>(&saved).unwrap().sanitized();
+    restore(&mut b);
+    assert_eq!(b.session.prefs.gridline_every, 50.0);
+}
+
+#[test]
+fn old_pref_files_keep_their_brightness() {
+    let mut a = app();
+    a.ui.brightness = Brightness::Light;
+    a.ui.engine_prefs = Value::Null;
+    restore(&mut a);
+    assert_eq!(a.session.prefs.ui_brightness, "light");
+}
+
+/// Performance › Graphics Processor (#306, #502): shown with its restart note, applied by OK
+/// and saved with the UI state under the key the desktop app reads before the window opens.
+#[test]
+fn graphics_processor_preference_shows_and_persists() {
+    fn texts(s: &egui::Shape, out: &mut Vec<String>) {
+        match s {
+            egui::Shape::Text(t) => out.push(t.galley.text().to_string()),
+            egui::Shape::Vec(v) => v.iter().for_each(|s| texts(s, out)),
+            _ => {}
+        }
+    }
+    let mut a = app();
+    open(&mut a, Some("Performance"));
+    let ctx = egui::Context::default();
+    crate::theme::install_fonts(&ctx);
+    // The window sizes itself on the first frame and draws on the second.
+    let mut out = ctx.run_ui(egui::RawInput::default(), |ui| show(&mut a, ui.ctx()));
+    out.textures_delta.clear();
+    let mut out = ctx.run_ui(egui::RawInput::default(), |ui| show(&mut a, ui.ctx()));
+    out.textures_delta.clear();
+    let mut shown = vec![];
+    out.shapes.iter().for_each(|c| texts(&c.shape, &mut shown));
+    assert!(shown.iter().any(|t| t.starts_with("Graphics Processor")), "{shown:?}");
+    assert!(shown.iter().any(|t| t == "Automatic"), "{shown:?}");
+    assert!(shown.iter().any(|t| t == "Applies the next time VectorCraft starts."), "{shown:?}");
+    a.ui.dialog.as_mut().unwrap().fields.insert("gpuPreference".into(), json!("highPerformance"));
+    assert!(!a.take_prefs_changed(), "nothing to write before OK");
+    confirm(&mut a).unwrap();
+    assert!(a.take_prefs_changed(), "OK asks the host to write the preferences file");
+    assert!(!a.take_prefs_changed());
+    assert_eq!(a.session.prefs.gpu_preference, "highPerformance");
+    let saved: Value = serde_json::from_slice(&serde_json::to_vec(&a.ui).unwrap()).unwrap();
+    assert_eq!(saved["engine_prefs"]["gpuPreference"], json!("highPerformance"));
+}
+
+/// User Interface › System Title Bar: shown with its next-launch note, applied by OK and
+/// saved with the UI state under the key the desktop app reads before the window opens.
+#[test]
+fn system_title_bar_preference_shows_and_persists() {
+    fn texts(s: &egui::Shape, out: &mut Vec<String>) {
+        match s {
+            egui::Shape::Text(t) => out.push(t.galley.text().to_string()),
+            egui::Shape::Vec(v) => v.iter().for_each(|s| texts(s, out)),
+            _ => {}
+        }
+    }
+    let mut a = app();
+    open(&mut a, Some("User Interface"));
+    let ctx = egui::Context::default();
+    crate::theme::install_fonts(&ctx);
+    // The window sizes itself on the first frame and draws on the second.
+    let mut out = ctx.run_ui(egui::RawInput::default(), |ui| show(&mut a, ui.ctx()));
+    out.textures_delta.clear();
+    let mut out = ctx.run_ui(egui::RawInput::default(), |ui| show(&mut a, ui.ctx()));
+    out.textures_delta.clear();
+    let mut shown = vec![];
+    out.shapes.iter().for_each(|c| texts(&c.shape, &mut shown));
+    let supported = cfg!(all(not(target_arch = "wasm32"), not(target_os = "macos")));
+    assert_eq!(shown.iter().any(|t| t == "System Title Bar"), supported, "{shown:?}");
+    assert_eq!(shown.iter().any(|t| t == "Applies the next time VectorCraft starts."), supported, "{shown:?}");
+    a.ui.dialog.as_mut().unwrap().fields.insert("systemTitleBar".into(), json!(true));
+    confirm(&mut a).unwrap();
+    assert!(a.session.prefs.system_title_bar);
+    let saved: Value = serde_json::from_slice(&serde_json::to_vec(&a.ui).unwrap()).unwrap();
+    assert_eq!(saved["engine_prefs"]["systemTitleBar"], json!(true));
+}
+
+/// Performance › Linux Display Server (#2028): on Linux it shows the drawing-tablet note, and
+/// X11 (XWayland) When a Pen Is Attached is applied by OK and saved under the key the desktop
+/// app reads before the window opens.
+#[test]
+fn linux_display_server_offers_the_pen_choice() {
+    fn texts(s: &egui::Shape, out: &mut Vec<String>) {
+        match s {
+            egui::Shape::Text(t) => out.push(t.galley.text().to_string()),
+            egui::Shape::Vec(v) => v.iter().for_each(|s| texts(s, out)),
+            _ => {}
+        }
+    }
+    let mut a = app();
+    open(&mut a, Some("Performance"));
+    let ctx = egui::Context::default();
+    crate::theme::install_fonts(&ctx);
+    // The window sizes itself on the first frame and draws on the second.
+    let mut out = ctx.run_ui(egui::RawInput::default(), |ui| show(&mut a, ui.ctx()));
+    out.textures_delta.clear();
+    let mut out = ctx.run_ui(egui::RawInput::default(), |ui| show(&mut a, ui.ctx()));
+    out.textures_delta.clear();
+    let mut shown = vec![];
+    out.shapes.iter().for_each(|c| texts(&c.shape, &mut shown));
+    let linux = cfg!(target_os = "linux");
+    assert_eq!(shown.iter().any(|t| t.starts_with("Linux Display Server")), linux, "{shown:?}");
+    let note = "If a drawing tablet's pen doesn't draw, choose an X11 (XWayland) option.";
+    assert_eq!(shown.iter().any(|t| t == note), linux, "{shown:?}");
+    a.ui.dialog.as_mut().unwrap().fields.insert("linuxDisplayServer".into(), json!("x11WithPen"));
+    confirm(&mut a).unwrap();
+    assert_eq!(a.session.prefs.linux_display_server, "x11WithPen");
+    let saved: Value = serde_json::from_slice(&serde_json::to_vec(&a.ui).unwrap()).unwrap();
+    assert_eq!(saved["engine_prefs"]["linuxDisplayServer"], json!("x11WithPen"));
+}
+
+/// #1866: the category shown is highlighted in the list while the pointer is elsewhere.
+#[test]
+fn the_category_shown_is_highlighted() {
+    fn rects(s: &egui::Shape, out: &mut Vec<(egui::Rect, egui::Color32)>) {
+        match s {
+            egui::Shape::Rect(r) => out.push((r.rect, r.fill)),
+            egui::Shape::Vec(v) => v.iter().for_each(|s| rects(s, out)),
+            _ => {}
+        }
+    }
+    let mut a = app();
+    open(&mut a, Some("Units"));
+    let ctx = egui::Context::default();
+    crate::theme::install_fonts(&ctx);
+    // The window sizes itself on the first frame and draws on the second.
+    let mut out = ctx.run_ui(egui::RawInput::default(), |ui| show(&mut a, ui.ctx()));
+    out.textures_delta.clear();
+    let mut out = ctx.run_ui(egui::RawInput::default(), |ui| show(&mut a, ui.ctx()));
+    out.textures_delta.clear();
+    let mut shown = vec![];
+    out.shapes.iter().for_each(|c| rects(&c.shape, &mut shown));
+    // The list's rows, top to bottom: only the fourth (Units) is filled.
+    let rows: Vec<_> = shown.iter().filter(|(r, _)| r.width() == 184.0 && r.height() < 30.0).collect();
+    assert_eq!(rows.len(), PREF_CATEGORIES.len(), "{shown:?}");
+    let filled: Vec<usize> = rows.iter().enumerate().filter(|(_, (_, c))| c.a() > 0).map(|(i, _)| i).collect();
+    assert_eq!(filled, vec![3], "{rows:?}");
+}
+
+/// Units › Numbers Without Units Are Points (#394): the preference reaches the fields when it
+/// changes, and its checkbox is dimmed unless a unit is Picas.
+#[test]
+fn numbers_without_units_are_points_reaches_the_fields_and_dims_without_picas() {
+    let mut a = app();
+    let ctx = egui::Context::default();
+    crate::theme::install_fonts(&ctx);
+    let frame = |a: &mut VectorcraftApp| {
+        let mut out = ctx.run_ui(egui::RawInput::default(), |ui| {
+            apply_runtime(a, ui.ctx());
+            show(a, ui.ctx());
+        });
+        out.textures_delta.clear();
+    };
+    let read = |ctx: &egui::Context| widgets::typed_unit(ctx, vectorcraft_doc::Unit::Picas);
+    frame(&mut a);
+    assert_eq!(read(&ctx), vectorcraft_doc::Unit::Points, "on by default");
+    a.run("prefs.set", json!({"key": "numbersWithoutUnitsArePoints", "value": false})).unwrap();
+    frame(&mut a);
+    assert_eq!(read(&ctx), vectorcraft_doc::Unit::Picas, "off");
+    // The checkbox: dimmed with every unit in points, enabled once a unit is Picas.
+    open(&mut a, Some("Units"));
+    let d = a.ui.dialog.as_mut().unwrap();
+    assert!(!picas_in_use(d), "dimmed in points");
+    d.fields.insert("unitsStroke".into(), json!("picas"));
+    assert!(picas_in_use(d), "enabled with a unit in picas");
+}
+
+/// 0.5.0 saved `powerSaving` for everyone (its default): it reads as Automatic, while the
+/// choices this version offers are kept (#502).
+#[test]
+fn a_graphics_processor_this_version_does_not_offer_reads_as_automatic() {
+    for (saved, read) in [("powerSaving", "automatic"), ("turbo", "automatic"), ("lowPower", "lowPower"), ("highPerformance", "highPerformance")]
+    {
+        let mut a = app();
+        a.ui.engine_prefs = json!({"gpuPreference": saved});
+        restore(&mut a);
+        assert_eq!(a.session.prefs.gpu_preference, read, "{saved}");
+    }
+}
+
+#[test]
+fn every_category_renders_fields() {
+    for c in PREF_CATEGORIES {
+        assert!(PREF_SPECS.iter().any(|s| s.category == *c));
+    }
+}
+
+/// Preferences › Type › Show Font Names in English (#394): OK on the dialog stores the flag the
+/// font menus read (Character panel, Type → Font).
+#[test]
+fn show_font_names_in_english_dialog_ok_stores_the_flag() {
+    let mut a = app();
+    assert!(a.session.prefs.font_names_in_english);
+    open(&mut a, Some("Type"));
+    assert_eq!(a.ui.dialog.as_ref().unwrap().str("__category"), "Type");
+    a.ui.dialog.as_mut().unwrap().fields.insert("fontNamesInEnglish".into(), json!(false));
+    confirm(&mut a).unwrap();
+    assert!(a.ui.dialog.is_none());
+    assert!(!a.session.prefs.font_names_in_english);
+    assert!(!crate::font_menu::MenuLook::of(&a).english_names);
+}
+
+/// Preferences › Hyphenation › Exceptions (#394): OK on the dialog pushes the list into the
+/// hyphenator the same way `prefs.set` does (no need to drive the live Preferences window).
+#[test]
+fn hyphenation_exceptions_dialog_ok_reaches_the_hyphenator() {
+    struct Clear;
+    impl Drop for Clear {
+        fn drop(&mut self) {
+            vectorcraft_text::set_hyphenation_exceptions("");
+        }
+    }
+    let _clear = Clear;
+    let mut a = app();
+    open(&mut a, Some("Hyphenation"));
+    let d = a.ui.dialog.as_mut().unwrap();
+    assert_eq!(d.str("__category"), "Hyphenation");
+    d.fields.insert("hyphenationExceptions".into(), json!("typography, hap-pen"));
+    confirm(&mut a).unwrap();
+    assert!(a.ui.dialog.is_none());
+    assert_eq!(a.session.prefs.hyphenation_exceptions, "typography, hap-pen");
+    assert_eq!(vectorcraft_text::hyphenation_exceptions(), "typography, hap-pen");
+    assert!(vectorcraft_text::hyphen::hyphen_points("typography").is_empty());
+    assert_eq!(vectorcraft_text::hyphen::hyphen_points("happen"), vec![3]);
+}