Add getOverlay method to access sketch and selection layers

test/spec/ol/interaction/draw.test.js

@@ -1060,6 +1060,13 @@ describe('ol.interaction.Draw', function() {
     });
   });
 
+  describe('#getOverlay', function() {
+    it('returns the feature overlay layer', function() {
+      const draw = new Draw({});
+      expect (draw.getOverlay()).to.eql(draw.overlay_);
+    });
+  });
+
   describe('createRegularPolygon', function() {
     it('creates a regular polygon in Circle mode', function() {
       const draw = new Draw({

test/spec/ol/interaction/modify.test.js

@@ -712,4 +712,13 @@ describe('ol.interaction.Modify', function() {
     });
   });
 
+  describe('#getOverlay', function() {
+    it('returns the feature overlay layer', function() {
+      const modify = new Modify({
+        features: new Collection()
+      });
+      expect (modify.getOverlay()).to.eql(modify.overlay_);
+    });
+  });
+
 });

test/spec/ol/interaction/select.test.js

@@ -442,4 +442,11 @@ describe('ol.interaction.Select', function() {
       });
     });
   });
+
+  describe('#getOverlay', function() {
+    it('returns the feature overlay layer', function() {
+      const select = new Select();
+      expect (select.getOverlay()).to.eql(select.featureOverlay_);
+    });
+  });
 });