test: fix test-buffer-zero-fill-cli to be effective

PR-URL: https://github.com/nodejs/node/pull/60623
Reviewed-By: Rafael Gonzaga <rafael.nunu@hotmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

test/parallel/test-buffer-zero-fill-cli.js

@@ -14,6 +14,13 @@ function isZeroFilled(buf) {
   return true;
 }
 
+// We have to consume the data from the pool as otherwise
+// we would be testing what's in snapshot, which is zero-filled
+// regardless of the flag presence, and we want to test the flag
+for (let i = 0; i < 8; i++) {
+  assert(isZeroFilled(Buffer.allocUnsafe(1024)));
+}
+
 // This can be somewhat unreliable because the
 // allocated memory might just already happen to
 // contain all zeroes. The test is run multiple
@@ -22,7 +29,8 @@ for (let i = 0; i < 50; i++) {
   const bufs = [
     Buffer.alloc(20),
     Buffer.allocUnsafe(20),
-    Buffer.allocUnsafeSlow(20),
+    Buffer.allocUnsafeSlow(20), // Heap
+    Buffer.allocUnsafeSlow(128), // Alloc
     Buffer(20),
   ];
   for (const buf of bufs) {