test: the off-page paragraph test compares the gap with the same pixels without Edit text (#3061)

Review on #3070: the gap between pages isn't one colour on every platform;
on ubuntu CI the pixel at x = 416 was one level off the fixed sample taken
40 px from the page's right edge. The test now takes a screenshot of the
same pages before Edit text is on (no paragraph outline), checks that the
pages stay where they were, and compares every gap pixel with the same
pixel there. Removing either clip still fails it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01R3niW7kVeT8mi7TpWc8eAJ

crates/ui-egui/tests/editing.rs

@@ -4856,13 +4856,20 @@ fn a_paragraph_running_off_its_page_edits_without_covering_the_next_page() {
         app
     });
     h.run_steps(4);
-    assert!(h.state_mut().execute("edit.edit_text"));
     h.state_mut().views[0].fit = pdfcraft_ui_egui::canvas::Fit::Page;
     h.run_steps(4);
+    let rects =
+        |h: &Harness<'static, PdfCraftApp>| (h.state().views[0].page_screen_rect(0).unwrap(), h.state().views[0].page_screen_rect(1).unwrap());
+    // The same pages without Edit text, so without the paragraph's outline: what the gap looks
+    // like there, pixel by pixel (review on #3070: it isn't one colour on every platform).
+    let (first, second) = rects(&h);
+    let plain = h.render().unwrap();
+    assert!(h.state_mut().execute("edit.edit_text"));
+    h.run_steps(4);
+    assert_eq!(rects(&h), (first, second), "Edit text keeps the pages where they were");
     let id = h.state().views[0].id;
     let info = h.state().session.get(id).unwrap().info.pages[0].clone();
-    let (first, second) = (h.state().views[0].page_screen_rect(0).unwrap(), h.state().views[0].page_screen_rect(1).unwrap());
-    shown_on_its_page_only(&mut h, first, second, "the paragraph's outline");
+    shown_on_its_page_only(&mut h, &plain, first, second, "the paragraph's outline");
     let v = info.user_to_view(200.0, 378.0);
     let p = first.min + egui::vec2(v[0], v[1]) * (first.width() / info.width);
     h.hover_at(p);
@@ -4881,7 +4888,7 @@ fn a_paragraph_running_off_its_page_edits_without_covering_the_next_page() {
         h.state().views[0].line_editor.as_ref().is_some_and(|e| e.page == 0 && e.text.contains("line 50")),
         "the paragraph's off-page lines are in it"
     );
-    shown_on_its_page_only(&mut h, first, second, "the open editor");
+    shown_on_its_page_only(&mut h, &plain, first, second, "the open editor");
     // Scrolled up past the tool bar, the editor stays inside the document area.
     let viewport = h.state().views[0].viewport_rect();
     let above = viewport.top() - 3.0;
@@ -4904,15 +4911,15 @@ fn a_paragraph_running_off_its_page_edits_without_covering_the_next_page() {
 }
 
 /// Between pages `first` and `second`, and on `second` above its own text, across where page
-/// 1's paragraph is: what is there without it (the gap's colour right of the paragraph, white
-/// paper).
-fn shown_on_its_page_only(h: &mut Harness<'static, PdfCraftApp>, first: egui::Rect, second: egui::Rect, what: &str) {
+/// 1's paragraph is: what is there without it (the gap as `plain` shows it without Edit text,
+/// white paper).
+fn shown_on_its_page_only(h: &mut Harness<'static, PdfCraftApp>, plain: &image::RgbaImage, first: egui::Rect, second: egui::Rect, what: &str) {
     let shot = h.render().unwrap();
     let pixel = |x: f32, y: f32| shot.get_pixel(x as u32, y as u32).0;
-    let gap = pixel(first.right() - 40.0, (first.bottom() + second.top()) / 2.0);
+    let gap_y = (first.bottom() + second.top()) / 2.0;
     for x in (first.left() as u32 + 70)..(first.left() as u32 + 420) {
         let x = x as f32;
-        assert_eq!(pixel(x, (first.bottom() + second.top()) / 2.0), gap, "{what}: between the pages at x = {x}");
+        assert_eq!(pixel(x, gap_y), plain.get_pixel(x as u32, gap_y as u32).0, "{what}: between the pages at x = {x}");
         for dy in [4.0, 20.0, 40.0] {
             let [r, g, b, _] = pixel(x, second.top() + dy);
             assert!(r > 240 && g > 240 && b > 240, "{what}: page 2 at {x}, +{dy}: {r},{g},{b}");