Add carousel Slack alerts for nightly Maestro failures (#11645)

.github/scripts/frame-slack-screenshots.test.mjs

@@ -0,0 +1,58 @@
+import assert from 'node:assert/strict'
+import fs from 'node:fs'
+import os from 'node:os'
+import path from 'node:path'
+import test from 'node:test'
+
+import sharp from 'sharp'
+
+import {frameSlackScreenshots} from './frame-slack-screenshots.mjs'
+
+test('frames Slack screenshots as 4:3 PNGs', async t => {
+  const root = fs.mkdtempSync(path.join(os.tmpdir(), 'maestro-slack-frame-'))
+  t.after(() => fs.rmSync(root, {recursive: true, force: true}))
+  const source = path.join(root, 'source.png')
+  const input = path.join(root, 'input.json')
+  const output = path.join(root, 'output.json')
+  const outputDir = path.join(root, 'images')
+  await sharp({
+    create: {
+      width: 2,
+      height: 4,
+      channels: 3,
+      background: '#ffffff',
+    },
+  })
+    .png()
+    .toFile(source)
+  fs.writeFileSync(
+    input,
+    JSON.stringify({
+      file_uploads: [
+        {
+          file: source,
+          filename: '1-android-login.png',
+          alt_text: 'Android failure screenshot for login',
+        },
+      ],
+    }),
+  )
+
+  await frameSlackScreenshots({inputPath: input, outputPath: output, outputDir})
+
+  const payload = JSON.parse(fs.readFileSync(output, 'utf8'))
+  const {data, info} = await sharp(payload.file_uploads[0].file)
+    .raw()
+    .toBuffer({resolveWithObject: true})
+  const pixelAt = (x, y) => {
+    const offset = (y * info.width + x) * info.channels
+    return Array.from(data.subarray(offset, offset + 3))
+  }
+
+  assert.equal(info.width, 1600)
+  assert.equal(info.height, 1200)
+  assert.deepEqual(pixelAt(0, 0), [248, 248, 248])
+  assert.deepEqual(pixelAt(800, 600), [255, 255, 255])
+  assert.equal(payload.file_uploads[0].filename, '1-android-login.png')
+  assert.equal(payload.file_uploads[0].highlight_type, 'png')
+})