test: different sizes of actual and expected

server/src/compare.test.js

@@ -1,5 +1,6 @@
 import fs from "fs/promises";
 import { compare } from "./compare.js";
+import { PNG } from "pngjs";
 
 describe("compare", () => {
   it("returns the number of pixels that differ", async () => {
@@ -14,4 +15,20 @@ describe("compare", () => {
     expect(result.actual).toStrictEqual(actual);
     expect(result.diff).toStrictEqual(expectedDiff);
   });
+
+  it("enlarges images to be able to create diffs", async () => {
+    const expected = emptyPNG(1920, 1024);
+    const actual = emptyPNG(2000, 800);
+
+    const result = await compare(expected, actual);
+
+    const diff = PNG.sync.read(result.diff);
+    expect(diff.width).toStrictEqual(2000);
+    expect(diff.height).toStrictEqual(1024);
+  });
 });
+
+function emptyPNG(width, height) {
+  const png = new PNG({ width, height });
+  return PNG.sync.write(png);
+}