test: improve WASI start() coverage

This commit adds additional test cases to
test-wasi-start-validation.js, which gets the JS test coverage
of start() to 100%.
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>

Author: cjihrig

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

@@ -1,7 +1,7 @@
 // Flags: --experimental-wasi-unstable-preview0
 'use strict';
 
-require('../common');
+constcommon=require('../common');
 constassert=require('assert');
 const{WASI}=require('wasi');
 
@@ -30,3 +30,68 @@ const fixtures = require('../common/fixtures');
 );
 })();
 }
+
+(async()=>{
+constwasi=newWASI();
+constbufferSource=fixtures.readSync('simple.wasm');
+constwasm=awaitWebAssembly.compile(bufferSource);
+constinstance=awaitWebAssembly.instantiate(wasm);
+constvalues=[undefined,null,'foo',42,true,false,()=>{}];
+letcnt=0;
+
+// Mock instance.exports to trigger start() validation.
+Object.defineProperty(instance,'exports',{
+get(){returnvalues[cnt++];}
+});
+
+values.forEach((val)=>{
+assert.throws(
+()=>{wasi.start(instance);},
+{code: 'ERR_INVALID_ARG_TYPE',message: /\binstance\.exports\b/}
+);
+});
+})();
+
+(async()=>{
+constwasi=newWASI();
+constbufferSource=fixtures.readSync('simple.wasm');
+constwasm=awaitWebAssembly.compile(bufferSource);
+constinstance=awaitWebAssembly.instantiate(wasm);
+
+// Mock instance.exports.memory to bypass start() validation.
+Object.defineProperty(instance,'exports',{
+get(){
+return{
+memory: newWebAssembly.Memory({initial: 1})
+};
+}
+});
+
+wasi.start(instance);
+assert.throws(
+()=>{wasi.start(instance);},
+{
+code: 'ERR_WASI_ALREADY_STARTED',
+message: /^WASIinstancehasalreadystarted$/
+}
+);
+})();
+
+(async()=>{
+constwasi=newWASI();
+constbufferSource=fixtures.readSync('simple.wasm');
+constwasm=awaitWebAssembly.compile(bufferSource);
+constinstance=awaitWebAssembly.instantiate(wasm);
+
+// Mock instance.exports to bypass start() validation.
+Object.defineProperty(instance,'exports',{
+get(){
+return{
+memory: newWebAssembly.Memory({initial: 1}),
+__wasi_unstable_reactor_start: common.mustCall()
+};
+}
+});
+
+wasi.start(instance);
+})();