Fix flaky snapshot-testing (#4367)

* Fix flaky snapshot-testing

Signed-off-by: Matteo Collina <hello@matteocollina.com>

* moar logging

Signed-off-by: Matteo Collina <hello@matteocollina.com>

* fixup

Signed-off-by: Matteo Collina <hello@matteocollina.com>

* fixup

Signed-off-by: Matteo Collina <hello@matteocollina.com>

* fixup

Signed-off-by: Matteo Collina <hello@matteocollina.com>

---------

Signed-off-by: Matteo Collina <hello@matteocollina.com>

Author: mcollina

lib/mock/snapshot-recorder.js

@@ -4,6 +4,13 @@ const { writeFile, readFile, mkdir } = require('node:fs/promises')
 const { dirname, resolve } = require('node:path')
 const { InvalidArgumentError, UndiciError } = require('../core/errors')
 
+let crypto
+try {
+  crypto = require('node:crypto')
+} catch {
+  // Fallback if crypto is not available
+}
+
 /**
  * Formats a request for consistent snapshot storage
  * Caches normalized headers to avoid repeated processing
@@ -137,15 +144,45 @@ function normalizeHeaders (headers) {
 
 /**
  * Creates a hash key for request matching
+ * Properly orders headers to avoid conflicts and uses crypto hashing when available
  */
 function createRequestHash (request) {
   const parts = [
     request.method,
-    request.url,
-    JSON.stringify(request.headers, Object.keys(request.headers).sort()),
-    request.body || ''
+    request.url
   ]
-  return Buffer.from(parts.join('|')).toString('base64url')
+
+  // Process headers in a deterministic way to avoid conflicts
+  if (request.headers && typeof request.headers === 'object') {
+    const headerKeys = Object.keys(request.headers).sort()
+    for (const key of headerKeys) {
+      const lowerKey = key.toLowerCase()
+      const values = Array.isArray(request.headers[key])
+        ? request.headers[key]
+        : [request.headers[key]]
+
+      // Add header name
+      parts.push(lowerKey)
+
+      // Add all values for this header, sorted for consistency
+      for (const value of values.sort()) {
+        parts.push(String(value))
+      }
+    }
+  }
+
+  // Add body
+  parts.push(request.body || '')
+
+  const content = parts.join('|')
+
+  // Use crypto hash if available for better collision resistance
+  if (crypto && crypto.createHash) {
+    return crypto.createHash('sha256').update(content, 'utf8').digest('base64url')
+  }
+
+  // Fallback to base64 encoding
+  return Buffer.from(content).toString('base64url')
 }
 
 /**
@@ -291,30 +328,14 @@ class SnapshotRecorder {
     if (!snapshot) return undefined
 
     // Handle sequential responses
-    if (snapshot.responses && Array.isArray(snapshot.responses)) {
-      const currentCallCount = snapshot.callCount || 0
-      const responseIndex = Math.min(currentCallCount, snapshot.responses.length - 1)
-      snapshot.callCount = currentCallCount + 1
-
-      return {
-        ...snapshot,
-        response: snapshot.responses[responseIndex]
-      }
-    }
+    const currentCallCount = snapshot.callCount || 0
+    const responseIndex = Math.min(currentCallCount, snapshot.responses.length - 1)
+    snapshot.callCount = currentCallCount + 1
 
-    // Legacy format compatibility - convert single response to array format
-    if (snapshot.response && !snapshot.responses) {
-      snapshot.responses = [snapshot.response]
-      snapshot.callCount = 1
-      delete snapshot.response
-
-      return {
-        ...snapshot,
-        response: snapshot.responses[0]
-      }
+    return {
+      ...snapshot,
+      response: snapshot.responses[responseIndex]
     }
-
-    return snapshot
   }
 
   /**

test/snapshot-testing.js

@@ -347,9 +347,18 @@ describe('SnapshotAgent - Request Handling', () => {
     setGlobalDispatcher(recordingAgent)
 
     // Make multiple requests to record sequential responses
-    await request(`${origin}/api/test`)
-    await request(`${origin}/api/test`)
-    await request(`${origin}/api/test`)
+    {
+      const res = await request(`${origin}/api/test`)
+      await res.body.text()
+    }
+    {
+      const res = await request(`${origin}/api/test`)
+      await res.body.text()
+    }
+    {
+      const res = await request(`${origin}/api/test`)
+      await res.body.text()
+    }
 
     // Ensure all recordings are saved and verify the recording state
     await recordingAgent.saveSnapshots()
@@ -370,6 +379,7 @@ describe('SnapshotAgent - Request Handling', () => {
     })
 
     setupCleanup(t, { agent: playbackAgent })
+    setGlobalDispatcher(playbackAgent)
 
     // Ensure snapshots are loaded and call counts are reset before setting dispatcher
     await playbackAgent.loadSnapshots()
@@ -385,8 +395,6 @@ describe('SnapshotAgent - Request Handling', () => {
     assert.strictEqual(snapshots.length, 1, 'Should have exactly one snapshot')
     assert.strictEqual(snapshots[0].responses.length, 3, 'Should have three sequential responses')
 
-    setGlobalDispatcher(playbackAgent)
-
     // Test sequential responses
     const response1 = await request(`${origin}/api/test`)
     const body1 = await response1.body.text()