Add regression test for #3323, bug in layer dependency tracking (#3326)

Co-authored-by: Bart Louwers <bart@emeel.net>

test/fixtures/map/style_update_zoom_dependency/style.json

@@ -0,0 +1,13 @@
+{
+  "version": 8,
+  "sources": {},
+  "layers": [
+      {
+          "id": "background",
+          "type": "background",
+          "paint": {
+              "background-color": "#ff0000"
+          }
+      }
+  ]
+}

test/map/map.test.cpp

@@ -19,8 +19,10 @@
 #include <mbgl/storage/network_status.hpp>
 #include <mbgl/storage/online_file_source.hpp>
 #include <mbgl/storage/resource_options.hpp>
-#include <mbgl/style/image.hpp>
+#include <mbgl/style/expression/dsl.hpp>
 #include <mbgl/style/image_impl.hpp>
+#include <mbgl/style/image.hpp>
+#include <mbgl/style/layers/background_layer.hpp>
 #include <mbgl/style/layers/background_layer.hpp>
 #include <mbgl/style/layers/fill_layer.hpp>
 #include <mbgl/style/layers/raster_layer.hpp>
@@ -29,8 +31,8 @@
 #include <mbgl/style/sources/geojson_source.hpp>
 #include <mbgl/style/sources/image_source.hpp>
 #include <mbgl/style/sources/vector_source.hpp>
-#include <mbgl/style/style.hpp>
 #include <mbgl/style/style_impl.hpp>
+#include <mbgl/style/style.hpp>
 #include <mbgl/util/async_task.hpp>
 #include <mbgl/util/client_options.hpp>
 #include <mbgl/util/color.hpp>
@@ -1866,3 +1868,31 @@ TEST(Map, ObserveTileLifecycle) {
         EXPECT_FALSE(parsing);
     }
 }
+
+TEST(BackgroundLayer, StyleUpdateZoomDependency) {
+    using namespace mbgl::style::expression::dsl;
+
+    MapTest<> test;
+    test.map.getStyle().loadJSON(util::read_file("test/fixtures/map/style_update_zoom_dependency/style.json"));
+    test.map.jumpTo(CameraOptions().withZoom(0.0));
+
+    // Initial render: background should be red at zoom 0
+    test::checkImage("test/fixtures/map/style_update_zoom_dependency/initial_red",
+                     test.frontend.render(test.map).image,
+                     0.0006,
+                     0.1);
+
+    // Update background layer to use zoom-dependent color
+    auto layer = static_cast<style::BackgroundLayer*>(test.map.getStyle().getLayer("background"));
+    layer->setBackgroundColor(PropertyExpression<Color>(
+        interpolate(linear(), zoom(), 0.0, literal(Color::red()), 14.0, literal(Color::green()))));
+
+    test.frontend.render(test.map);
+
+    // Change zoom to 14 and re-render
+    test.map.jumpTo(CameraOptions().withZoom(14.0));
+    test::checkImage("test/fixtures/map/style_update_zoom_dependency/after_update_green",
+                     test.frontend.render(test.map).image,
+                     0.0006,
+                     0.1);
+}