Replaces raster.tests.js with new tests

Transforms the old rendering tests for the RasterSource
to the new rendering test approach.

rendering/cases/source-raster/main.js

@@ -0,0 +1,31 @@
+import Map from '../../../src/ol/Map.js';
+import View from '../../../src/ol/View.js';
+import ImageLayer from '../../../src/ol/layer/Image.js';
+import RasterSource from '../../../src/ol/source/Raster.js';
+import XYZ from '../../../src/ol/source/XYZ.js';
+
+const raster = new RasterSource({
+  sources: [new XYZ({
+    url: '/data/tiles/osm/{z}/{x}/{y}.png',
+    transition: 0
+  })],
+  operation: function(pixels) {
+    const pixel = pixels[0];
+    const red = pixel[0];
+    pixel[0] = pixel[2];
+    pixel[2] = red;
+    return pixel;
+  }
+});
+
+new Map({
+  layers: [new ImageLayer({source: raster})],
+  target: 'map',
+  view: new View({
+    center: [0, 0],
+    zoom: 0
+  })
+});
+
+render();
+