test: refactor test-child-process-spawnsync-maxbuf

This commit refactors test-child-process-spawnsync-maxbuf.js,
and adds testing for the case where maxBuffer is Infinity.

PR-URL: https://github.com/nodejs/node/pull/10769
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-child-process-spawnsync-maxbuf.js

@@ -1,9 +1,7 @@
 'use strict';
 require('../common');
 const assert = require('assert');
-
 const spawnSync = require('child_process').spawnSync;
-
 const msgOut = 'this is stdout';
 
 // This is actually not os.EOL?
@@ -14,14 +12,21 @@ const args = [
   `console.log("${msgOut}");`
 ];
 
-const options = {
-  maxBuffer: 1
-};
+// Verify that an error is returned if maxBuffer is surpassed.
+{
+  const ret = spawnSync(process.execPath, args, { maxBuffer: 1 });
+
+  assert.ok(ret.error, 'maxBuffer should error');
+  assert.strictEqual(ret.error.errno, 'ENOBUFS');
+  // We can have buffers larger than maxBuffer because underneath we alloc 64k
+  // that matches our read sizes.
+  assert.deepStrictEqual(ret.stdout, msgOutBuf);
+}
 
-const ret = spawnSync(process.execPath, args, options);
+// Verify that a maxBuffer size of Infinity works.
+{
+  const ret = spawnSync(process.execPath, args, { maxBuffer: Infinity });
 
-assert.ok(ret.error, 'maxBuffer should error');
-assert.strictEqual(ret.error.errno, 'ENOBUFS');
-// We can have buffers larger than maxBuffer because underneath we alloc 64k
-// that matches our read sizes
-assert.deepStrictEqual(ret.stdout, msgOutBuf);
+  assert.ifError(ret.error);
+  assert.deepStrictEqual(ret.stdout, msgOutBuf);
+}