add test - filtering by scale denominator on layer level

test/data/layer_scale_denom_style.xml

@@ -0,0 +1,21 @@
+<Map srs="+init=epsg:3857">
+    <Layer name="1" srs="+init=epsg:3857">
+        <Datasource>
+            <Parameter name="type">csv</Parameter>
+            <Parameter name="inline">
+                x, y
+                1, 2
+            </Parameter>
+        </Datasource>
+    </Layer>
+    <Layer name="2" srs="+init=epsg:3857" maximum-scale-denominator="200000">
+        <Datasource>
+            <Parameter name="type">csv</Parameter>
+            <Parameter name="inline">
+                x, y
+                3, 4
+                1, 4
+            </Parameter>
+        </Datasource>
+    </Layer>
+</Map>

test/unit/scale_denom_filter.cpp

@@ -0,0 +1,42 @@
+#include "catch.hpp"
+
+// mapnik
+#include <mapnik/load_map.hpp>
+
+// mapnik-vector-tile
+#include "vector_tile_processor.hpp"
+
+// libprotobuf
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-parameter"
+#pragma GCC diagnostic ignored "-Wsign-conversion"
+#include "vector_tile.pb.h"
+#pragma GCC diagnostic pop
+
+
+TEST_CASE("feature processor - filtering by scale denominator on layer level")
+{
+    mapnik::Map map(256, 256);
+    mapnik::load_map(map, "test/data/layer_scale_denom_style.xml");
+    mapnik::vector_tile_impl::processor ren(map);
+    const double scale_denom = 200000;
+
+    {
+        mapnik::vector_tile_impl::tile out_tile = ren.create_tile(
+            2048, 2047, 12, 4096, 0, scale_denom);
+        vector_tile::Tile tile;
+        REQUIRE(tile.ParseFromString(out_tile.get_buffer()));
+        REQUIRE(2 == tile.layers_size());
+        CHECK(1 == tile.layers(0).features_size());
+        CHECK(2 == tile.layers(1).features_size());
+    }
+    {
+        // One layer is filtered out after change of scale denominator.
+        mapnik::vector_tile_impl::tile out_tile = ren.create_tile(
+            2048, 2047, 12, 4096, 0, scale_denom * 2.0);
+        vector_tile::Tile tile;
+        REQUIRE(tile.ParseFromString(out_tile.get_buffer()));
+        REQUIRE(1 == tile.layers_size());
+        CHECK(1 == tile.layers(0).features_size());
+    }
+}