add tests

test/data.dart

+String geojsonNestedGeometryCollection = """{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {"name": "collection"},
+      "geometry": {
+        "type": "GeometryCollection",
+        "geometries": [
+          {
+            "type": "GeometryCollection",
+            "geometries": [
+              {
+                "type": "Point",
+                "coordinates": [0, 0]
+              },
+              {
+                "type": "Point",
+                "coordinates": [1, 1]
+              }
+            ]
+          },
+          {
+            "type": "Point",
+            "coordinates": [0, 0]
+          }
+        ]
+      }
+    }
+  ]
+}""";
 String geojsonPoint = """{
   "type": "FeatureCollection",
   "features": [

test/geojson_test.dart

@@ -7,6 +7,29 @@ import "package:test/test.dart";
 import 'data.dart';
 
 void main() {
+  test("nested geometrycollection", () async {
+    final features = await featuresFromGeoJson(geojsonNestedGeometryCollection);
+    expect(features.collection.length, 1);
+    final feature = features.collection[0];
+    expect(feature.type, GeoJsonFeatureType.geometryCollection);
+    final collection = feature.geometry as GeoJsonGeometryCollection;
+    expect(collection.geometries.length, 2);
+    expect(
+        collection.geometries[0].type, GeoJsonFeatureType.geometryCollection);
+    final innerCollection =
+        collection.geometries[0].geometry as GeoJsonGeometryCollection;
+    expect(innerCollection.geometries.length, 2);
+    expect(
+        innerCollection.geometries
+            .every((element) => element.type == GeoJsonFeatureType.point),
+        true);
+
+    expect(collection.geometries[1].type, GeoJsonFeatureType.point);
+    final point = collection.geometries[1].geometry as GeoJsonPoint;
+    expect(point.geoPoint.latitude, 0);
+    expect(point.geoPoint.longitude, 0);
+  });
+
   test("point", () async {
     final features = await featuresFromGeoJson(geojsonPoint);
     expect(features.collection.length, 1);