Test renderer behavior for Zoomify zDirection

The zDirection addition to the Zoomify tile source only takes effect through
the renderer, so these two renderer cases are added to test the behavior.

zoomify-no-zdirection expects the default behavior.
zoomify-zdirection expects the tiles for the next better resolution.

rendering/cases/zoomify-no-zdirection/main.js

@@ -0,0 +1,25 @@
+import Map from '../../../src/ol/Map.js';
+import View from '../../../src/ol/View.js';
+import TileLayer from '../../../src/ol/layer/Tile.js';
+import Zoomify from '../../../src/ol/source/Zoomify.js';
+
+const layer = new TileLayer({
+  source: new Zoomify({
+    url: '/data/tiles/zoomify/',
+    size: [200, 200],
+    tileSize: 100
+  })
+});
+
+new Map({
+  layers: [layer],
+  target: 'map',
+  view: new View({
+    resolutions: [2, 1],
+    extent: [0, -200, 200, 0],
+    center: [100, -100],
+    zoom: 0.4
+  })
+});
+
+render();

rendering/cases/zoomify-zdirection/main.js

@@ -0,0 +1,26 @@
+import Map from '../../../src/ol/Map.js';
+import View from '../../../src/ol/View.js';
+import TileLayer from '../../../src/ol/layer/Tile.js';
+import Zoomify from '../../../src/ol/source/Zoomify.js';
+
+const layer = new TileLayer({
+  source: new Zoomify({
+    url: '/data/tiles/zoomify/',
+    size: [200, 200],
+    tileSize: 100,
+    zDirection: -1
+  })
+});
+
+new Map({
+  layers: [layer],
+  target: 'map',
+  view: new View({
+    resolutions: [2, 1],
+    extent: [0, -200, 200, 0],
+    center: [100, -100],
+    zoom: 0.4
+  })
+});
+
+render();