[core] Add unit test for layer serialization

test/style/conversion/layer.test.cpp

@@ -4,6 +4,8 @@
 #include <mbgl/style/conversion/layer.hpp>
 #include <mbgl/style/layers/background_layer_impl.hpp>
 
+#include <rapidjson/prettywriter.h>
+
 using namespace mbgl;
 using namespace mbgl::style;
 using namespace mbgl::style::conversion;
@@ -11,7 +13,17 @@ using namespace std::literals::chrono_literals;
 
 std::unique_ptr<Layer> parseLayer(const std::string& src) {
     Error error;
-    return std::move(*convertJSON<std::unique_ptr<Layer>>(src, error));
+    auto layer = convertJSON<std::unique_ptr<Layer>>(src, error);
+    if (layer) return std::move(*layer);
+    return nullptr;
+}
+
+std::string stringifyLayer(const Value& value) {
+    rapidjson::StringBuffer s;
+    rapidjson::PrettyWriter<rapidjson::StringBuffer> writer(s);
+    writer.SetIndent(' ', 2u);
+    stringify(writer, value);
+    return s.GetString();
 }
 
 TEST(StyleConversion, LayerTransition) {
@@ -31,3 +43,85 @@ TEST(StyleConversion, LayerTransition) {
     ASSERT_EQ(500ms, *static_cast<BackgroundLayer*>(layer.get())->impl().paint
         .get<BackgroundColor>().options.delay);
 }
+
+TEST(StyleConversion, SerializeDefaults) {
+    auto layer = parseLayer(R"JSON({
+        "type": "background",
+        "id": "background"
+    })JSON");
+
+    EXPECT_NE(nullptr, layer);
+    auto value = layer->serialize();
+    EXPECT_NE(nullptr, value.getObject());
+    EXPECT_EQ(2u, value.getObject()->size());
+}
+
+TEST(StyleConversion, RoundtripWithTransitions) {
+    auto layer = parseLayer(R"JSON({
+        "type": "background",
+        "id": "background",
+        "paint": {
+            "background-color-transition": {
+                "duration": 400,
+                "delay": 500
+            }
+        }
+    })JSON");
+
+    EXPECT_NE(nullptr, layer);
+    auto value = layer->serialize();
+    EXPECT_NE(nullptr, value.getObject());
+    EXPECT_EQ(3u, value.getObject()->size());
+
+    auto roundTripped = parseLayer(stringifyLayer(value));
+    EXPECT_NE(nullptr, roundTripped);
+    auto roundTrippedValue = roundTripped->serialize();
+    EXPECT_NE(nullptr, roundTrippedValue.getObject());
+    EXPECT_EQ(3u, roundTrippedValue.getObject()->size());
+}
+
+TEST(StyleConversion, OverrideDefaults) {
+    auto layer = parseLayer(R"JSON({
+        "type": "symbol",
+        "id": "symbol",
+        "source": "composite",
+        "source-layer": "landmarks",
+        "filter": ["has", "monuments"],
+        "minzoom": 12,
+        "maxzoom": 18,
+        "layout": {
+            "visibility": "none",
+            "text-field": ["format",
+                            "Hello",
+                            ["image", ["get", "world"]],
+                            "Example", {"text-color": "rgba(128, 255, 39, 1)"}
+                          ],
+            "icon-image": ["image", ["get", "landmark_image"]],
+            "text-size": 24
+        },
+        "paint": {
+            "text-color": "turquoise",
+            "text-color-transition": {
+                "duration": 300,
+                "delay": 100
+            }
+        }
+    })JSON");
+
+    EXPECT_NE(nullptr, layer);
+    auto value = layer->serialize();
+    EXPECT_NE(nullptr, value.getObject());
+    const auto& object = *(value.getObject());
+    EXPECT_EQ(9u, object.size());
+    EXPECT_EQ(4u, object.at("layout").getObject()->size());
+    EXPECT_EQ(2u, object.at("paint").getObject()->size());
+
+    auto roundTripped = parseLayer(stringifyLayer(value));
+    EXPECT_NE(nullptr, roundTripped);
+    auto roundTrippedValue = roundTripped->serialize();
+    const auto& roundTrippedObject = *(roundTrippedValue.getObject());
+    EXPECT_NE(nullptr, roundTrippedValue.getObject());
+    EXPECT_EQ(9u, roundTrippedObject.size());
+    EXPECT_EQ(4u, roundTrippedObject.at("layout").getObject()->size());
+    EXPECT_EQ(2u, roundTrippedObject.at("paint").getObject()->size());
+}