Keep track of when a layer is unrendered

test/browser/spec/ol/layer/Layer.test.js

@@ -4,6 +4,9 @@ import Map from '../../../../../src/ol/Map.js';
 import Property from '../../../../../src/ol/layer/Property.js';
 import RenderEvent from '../../../../../src/ol/render/Event.js';
 import Source from '../../../../../src/ol/source/Source.js';
+import TileLayer from '../../../../../src/ol/layer/Tile.js';
+import View from '../../../../../src/ol/View.js';
+import XYZ from '../../../../../src/ol/source/XYZ.js';
 import {get as getProjection} from '../../../../../src/ol/proj.js';
 
 describe('ol/layer/Layer', function () {
@@ -619,6 +622,77 @@ describe('ol/layer/Layer', function () {
     });
   });
 
+  describe('unrender()', () => {
+    /** @type {Map} */
+    let map;
+
+    /** @type {TileLayer} */
+    let layer;
+
+    /** HTMLDivElement */
+    let target;
+
+    beforeEach((done) => {
+      target = document.createElement('div');
+      target.style.width = '100px';
+      target.style.height = '100px';
+      document.body.appendChild(target);
+
+      layer = new TileLayer({
+        source: new XYZ({
+          url: 'spec/ol/data/osm-0-0-0.png',
+        }),
+      });
+
+      map = new Map({
+        target: target,
+        layers: [layer],
+        view: new View({
+          center: [0, 0],
+          zoom: 0,
+        }),
+      });
+
+      map.once('rendercomplete', () => done());
+    });
+
+    afterEach(() => {
+      map.setTarget(null);
+      document.body.removeChild(target);
+    });
+
+    it('is called when a layer goes from visible to not visible', () => {
+      const spy = sinon.spy(layer, 'unrender');
+      map.renderSync();
+      expect(spy.callCount).to.be(0);
+
+      layer.setVisible(false);
+      map.renderSync();
+      expect(spy.callCount).to.be(1);
+    });
+
+    it('is called when a layer is removed from the map', () => {
+      const spy = sinon.spy(layer, 'unrender');
+      map.renderSync();
+      expect(spy.callCount).to.be(0);
+
+      map.removeLayer(layer);
+      map.renderSync();
+      expect(spy.callCount).to.be(1);
+    });
+
+    it('is called when a layer goes out of range', () => {
+      const spy = sinon.spy(layer, 'unrender');
+      map.renderSync();
+      expect(spy.callCount).to.be(0);
+
+      layer.setMaxZoom(3);
+      map.getView().setZoom(4);
+      map.renderSync();
+      expect(spy.callCount).to.be(1);
+    });
+  });
+
   describe('map property', () => {
     it('is set when a layer is added to a map', () => {
       const map = new Map({});