Add tests for WebKit Bug 242740: simultaneous imports with top-level await

test/language/module-code/top-level-await/simultaneous-imports-race-condition.js

@@ -0,0 +1,46 @@
+// Copyright (C) 2025 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-moduleevaluation
+description: >
+  Simultaneous imports of a module with top-level await should all wait for evaluation to complete
+info: |
+  Module Evaluation
+    1. If module.[[TopLevelCapability]] is not empty, then
+       a. Return module.[[TopLevelCapability]].[[Promise]].
+
+  When multiple modules simultaneously import the same module with top-level await,
+  all import promises should wait for the module's top-level capability to resolve.
+
+flags: [module, async]
+features: [top-level-await, dynamic-import]
+---*/
+
+let continueExecution;
+globalThis.promise = new Promise((resolve) => continueExecution = resolve);
+
+const executionStartPromise = new Promise((resolve) => globalThis.executionStarted = resolve);
+
+const importPromises = [];
+
+for (let i = 0; i < 3; i++) {
+  importPromises.push(import("./simultaneous-imports-race-condition_FIXTURE.js"));
+}
+
+await executionStartPromise;
+
+continueExecution();
+
+const results = await Promise.all(importPromises);
+
+const firstResult = results[0];
+for (let i = 1; i < results.length; i++) {
+  assert.sameValue(results[i], firstResult,
+    `Import ${i} should return the same module namespace`);
+}
+
+assert.sameValue(firstResult.exportedValue, "success", "Exported value should be correct");
+assert.sameValue(firstResult.importCount, 3, "Module should have been imported 3 times");
+
+$DONE(); 

test/language/module-code/top-level-await/simultaneous-imports-race-condition_FIXTURE.js

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+// Copyright (C) 2025 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+globalThis.executionStarted();
+
+let importCount = 0;
+importCount++;
+
+await globalThis.promise;
+
+export const exportedValue = "success";
+export { importCount };