Module source object host invariant test

test/staging/source-phase-imports/module-source-prototype-chain.js

@@ -0,0 +1,35 @@
+// Copyright (C) 2025 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+description: >
+  The [[ModuleSource]] object's [[Prototype]]'s [[Prototype]] must be
+  %AbstractModuleSource%.prototype.
+esid: sec-abstract-module-records
+info: |
+  Table 3: Module Record Fields
+
+  [[ModuleSource]]
+  The Module Source Object corresponding to this source Module Record's
+  source phase, or ~empty~ if it is not available for this module kind.
+  When not ~empty~, it must be an object whose initial [[Prototype]] is
+  an object whose initial [[Prototype]] is %AbstractModuleSource%.prototype.
+
+features: [source-phase-imports, source-phase-imports-module-source]
+flags: [async]
+includes: [asyncHelpers.js]
+---*/
+
+asyncTest(async function () {
+  const moduleSource = await import.source('<module source>');
+
+  assert.sameValue(typeof moduleSource, 'object',
+    'import.source() must resolve to an object');
+
+  const proto = Object.getPrototypeOf(moduleSource);
+  assert.notSameValue(proto, null,
+    'The [[ModuleSource]] object must have a [[Prototype]]');
+
+  const protoProto = Object.getPrototypeOf(proto);
+  assert.sameValue(protoProto, $262.AbstractModuleSource.prototype,
+    'The [[Prototype]] of the [[ModuleSource]] object\'s [[Prototype]] must be %AbstractModuleSource%.prototype');
+});