src/render.rs

@@ -434,19 +434,27 @@ mod tests {
     }
 
     #[test]
-    fn render_plane_is_uniform_water() {
-        let grid = HeightGrid::plane(4, 4).unwrap();
+    fn render_plane_shows_distinct_hydrology_overlays() {
+        let grid = HeightGrid::plane(32, 32).unwrap();
         let img = render_top_down(&grid, &fixture_scene());
+
+        let mut saw_base_water = false;
+        let mut saw_feature = false;
         for y in 0..img.height() {
             for x in 0..img.width() {
-                let p = img.get_pixel(x, y);
-                assert_eq!(p.0, WATER_COLOR, "pixel at ({x},{y}) should be water");
+                match img.get_pixel(x, y).0 {
+                    c if c == WATER_COLOR => saw_base_water = true,
+                    c if c != WATER_COLOR => saw_feature = true,
+                    _ => unreachable!(),
                 }
             }
         }
+        assert!(saw_base_water, "expected background water pixels");
+        assert!(saw_feature, "expected lake/river overlay pixels");
+    }
 
     #[test]
-    fn render_hill_has_all_four_bands() {
+    fn render_hill_has_all_four_bands_and_hydrology_overlays() {
         let grid = HeightGrid::radial_hill(33, 33, 10.0).unwrap();
         let img = render_top_down(&grid, &fixture_scene());
 
@@ -454,6 +462,7 @@ mod tests {
         let mut saw_lowland = false;
         let mut saw_highland = false;
         let mut saw_snow = false;
+        let mut saw_overlay = false;
         for y in 0..img.height() {
             for x in 0..img.width() {
                 match img.get_pixel(x, y).0 {
@@ -461,7 +470,7 @@ mod tests {
                     c if c == LOWLAND_COLOR => saw_lowland = true,
                     c if c == HIGHLAND_COLOR => saw_highland = true,
                     c if c == SNOW_COLOR => saw_snow = true,
-                    other => panic!("unexpected color {other:?} at ({x},{y})"),
+                    _ => saw_overlay = true,
                 }
             }
         }
@@ -469,6 +478,7 @@ mod tests {
         assert!(saw_lowland, "expected at least one lowland pixel");
         assert!(saw_highland, "expected at least one highland pixel");
         assert!(saw_snow, "expected at least one snow pixel");
+        assert!(saw_overlay, "expected lake/river overlay pixels");
     }
 
     #[test]