Add snapshot test for text spacing/kerning (#7545)

crates/egui_demo_lib/tests/misc.rs

@@ -0,0 +1,26 @@
+use egui_kittest::Harness;
+
+#[test]
+fn test_kerning() {
+    for pixels_per_point in [1.0, 2.0] {
+        for theme in [egui::Theme::Dark, egui::Theme::Light] {
+            let mut harness = Harness::builder()
+                .with_pixels_per_point(pixels_per_point)
+                .with_theme(theme)
+                .build_ui(|ui| {
+                    ui.label("Thin spaces: −123 456 789");
+                    ui.label("Ligature: fi :)");
+                    ui.label("\ttabbed");
+                });
+            harness.run();
+            harness.fit_contents();
+            harness.snapshot(format!(
+                "image_blending/image_{theme}_x{pixels_per_point}",
+                theme = match theme {
+                    egui::Theme::Dark => "dark",
+                    egui::Theme::Light => "light",
+                }
+            ));
+        }
+    }
+}