refactor: use fixed regression pixel allowance

Author: TrySound

test/regression/compare.js

@@ -91,21 +91,6 @@ async function stopODiffServer(server) {
   }
 }
 
-/**
- * @param {string} file
- * @returns {Promise<number>}
- */
-async function readPngWidth(file) {
-  const handle = await fs.open(file);
-  try {
-    const header = Buffer.alloc(24);
-    await handle.read(header, 0, header.length, 0);
-    return header.readUInt32BE(16);
-  } finally {
-    await handle.close();
-  }
-}
-
 /**
  * @param {ReadonlyArray<string>} list
  * @param {{ workerCount?: number }=} options
@@ -181,14 +166,13 @@ export async function renderScreenshots(list, options = {}) {
 
 /**
  * @param {ReadonlyArray<string>} list
- * @param {{ ODiffServer?: ODiffServerConstructor, readWidth?: (file: string) => Promise<number> }=} options
+ * @param {{ ODiffServer?: ODiffServerConstructor }=} options
  * @returns {Promise<MatchResult[]>}
  */
 export async function compareScreenshots(list, options = {}) {
   /** @type {MatchResult[]} */
   const results = [];
   const ODiffServerClass = options.ODiffServer ?? ODiffServer;
-  const readWidth = options.readWidth ?? readPngWidth;
   const server = new ODiffServerClass();
   try {
     for (const name of list) {
@@ -215,9 +199,7 @@ export async function compareScreenshots(list, options = {}) {
       );
       let isMatch = result.match;
       if (!result.match && result.reason === 'pixel-diff') {
-        const width = await readWidth(originalPath);
-        const allowance = width <= 16 ? 3 : 4;
-        isMatch = result.diffCount <= allowance;
+        isMatch = result.diffCount <= 4;
         if (isMatch && process.env.NO_DIFF == null) {
           await fs.rm(diffPath, { force: true });
         }

test/regression/compare.test.js

@@ -33,13 +33,13 @@ describe('withCleanup', () => {
 });
 
 describe('compareScreenshots', () => {
-  test('preserves the width-dependent pixel allowance', async () => {
+  test('allows up to four differing pixels', async () => {
     const odiffResults = /** @type {import('odiff-bin').ODiffResult[]} */ ([
       { match: true },
       {
         match: false,
         reason: 'pixel-diff',
-        diffCount: 3,
+        diffCount: 4,
         diffPercentage: 1,
       },
       {
@@ -68,16 +68,15 @@ describe('compareScreenshots', () => {
 
     await expect(
       compareScreenshots(
-        ['exact.svg', 'small.svg', 'wide.svg', 'changed.svg', 'layout.svg'],
+        ['exact.svg', 'first.svg', 'second.svg', 'changed.svg', 'layout.svg'],
         {
           ODiffServer: FakeODiffServer,
-          readWidth: async (file) => (file.endsWith('small.svg.png') ? 16 : 17),
         },
       ),
     ).resolves.toEqual([
       { name: 'exact.svg', isMatch: true },
-      { name: 'small.svg', isMatch: true },
-      { name: 'wide.svg', isMatch: true },
+      { name: 'first.svg', isMatch: true },
+      { name: 'second.svg', isMatch: true },
       { name: 'changed.svg', isMatch: false },
       { name: 'layout.svg', isMatch: false },
     ]);