test: simplify test-wasi-start-validation.js

This commit removes an extra block scope, and avoid reading
the simple.wasm file for every test case.

PR-URL: #30972
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/wasi/test-wasi-start-validation.js

@@ -6,6 +6,7 @@ const assert = require('assert');
 const { WASI } = require('wasi');
 
 const fixtures = require('../common/fixtures');
+const bufferSource = fixtures.readSync('simple.wasm');
 
 {
   const wasi = new WASI();
@@ -17,23 +18,19 @@ const fixtures = require('../common/fixtures');
   );
 }
 
-{
+(async () => {
   const wasi = new WASI({});
-  (async () => {
-    const bufferSource = fixtures.readSync('simple.wasm');
-    const wasm = await WebAssembly.compile(bufferSource);
-    const instance = await WebAssembly.instantiate(wasm);
+  const wasm = await WebAssembly.compile(bufferSource);
+  const instance = await WebAssembly.instantiate(wasm);
 
-    assert.throws(
-      () => { wasi.start(instance); },
-      { code: 'ERR_INVALID_ARG_TYPE', message: /\bWebAssembly\.Memory\b/ }
-    );
-  })();
-}
+  assert.throws(
+    () => { wasi.start(instance); },
+    { code: 'ERR_INVALID_ARG_TYPE', message: /\bWebAssembly\.Memory\b/ }
+  );
+})();
 
 (async () => {
   const wasi = new WASI();
-  const bufferSource = fixtures.readSync('simple.wasm');
   const wasm = await WebAssembly.compile(bufferSource);
   const instance = await WebAssembly.instantiate(wasm);
   const values = [undefined, null, 'foo', 42, true, false, () => {}];
@@ -54,7 +51,6 @@ const fixtures = require('../common/fixtures');
 
 (async () => {
   const wasi = new WASI();
-  const bufferSource = fixtures.readSync('simple.wasm');
   const wasm = await WebAssembly.compile(bufferSource);
   const instance = await WebAssembly.instantiate(wasm);
 
@@ -79,7 +75,6 @@ const fixtures = require('../common/fixtures');
 
 (async () => {
   const wasi = new WASI();
-  const bufferSource = fixtures.readSync('simple.wasm');
   const wasm = await WebAssembly.compile(bufferSource);
   const instance = await WebAssembly.instantiate(wasm);