benchmark: stablize encode benchmark

- Increase the number of iteration to 1e6 to reduce flakes. 1e4
  can introduce flakes even when comparing the main branch
  against itself
- Replace the 1024 * 32 length test with 1024 * 8 since it would
  otherwise take too long to complete. Remove the 16 length test
  since it's not too different from 32.
- Check the results of the encoding methods at the end.

PR-URL: #46658
Reviewed-By: Darshan Sen <raisinten@gmail.com>

benchmark/util/text-encoder.js

@@ -1,10 +1,11 @@
 'use strict';
 
 const common = require('../common.js');
+const assert = require('assert');
 
 const bench = common.createBenchmark(main, {
-  len: [16, 32, 256, 1024, 1024 * 32],
-  n: [1e4],
+  len: [32, 256, 1024, 1024 * 8],
+  n: [1e6],
   type: ['one-byte-string', 'two-byte-string', 'ascii'],
   op: ['encode', 'encodeInto'],
 });
@@ -26,20 +27,24 @@ function main({ n, op, len, type }) {
   }
 
   const input = base.repeat(len);
-  const subarray = new Uint8Array(len);
-
-  bench.start();
-  switch (op) {
-    case 'encode': {
-      for (let i = 0; i < n; i++)
-        encoder.encode(input);
-      break;
-    }
-    case 'encodeInto': {
-      for (let i = 0; i < n; i++)
-        encoder.encodeInto(input, subarray);
-      break;
-    }
+  if (op === 'encode') {
+    const expected = encoder.encode(input);
+    let result;
+    bench.start();
+    for (let i = 0; i < n; i++)
+      result = encoder.encode(input);
+    bench.end(n);
+    assert.deepStrictEqual(result, expected);
+  } else {
+    const expected = new Uint8Array(len);
+    const subarray = new Uint8Array(len);
+    const expectedStats = encoder.encodeInto(input, expected);
+    let result;
+    bench.start();
+    for (let i = 0; i < n; i++)
+      result = encoder.encodeInto(input, subarray);
+    bench.end(n);
+    assert.deepStrictEqual(subarray, expected);
+    assert.deepStrictEqual(result, expectedStats);
   }
-  bench.end(n);
 }