test: add a simple test for import defer of a CJS module

test/es-module/test-cjs-defer-static-import-eval.mjs

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+// Flags: --js-defer-import-eval
+
+// Test that uses import.defer for a CJS module. It ensures that:
+//   1. the module is imported successfully;
+//   2. it's evaluated synchronously, regardless of the `defer` modifier;
+//   3. Evaluation of the imported module is deferred
+//      until first namespace access.
+
+import '../common/index.mjs';
+import * as assert from 'assert';
+
+// Import the CJS module with the `defer` modifier.
+import defer * as imported from '../fixtures/es-modules/module-cjs-deferred-eval.js';
+
+// At this point, the deferred module should not yet be evaluated. Initialize
+// the `eval_list`, which will be populated only when the module is evaluated
+// for the first time, triggered by namespace access below.
+globalThis.eval_list = [];
+
+// Additionally check that the exported properties `foo` and `identifier`
+// are defined and have their values assigned at this point.
+assert.strictEqual(imported.foo, 42);
+assert.strictEqual(imported.identifier, 'package-type-commonjs');
+
+// Check that the module has been evaluated at this point,
+// also that it's not evaluated more than once.
+assert.deepStrictEqual(['defer-1'], globalThis.eval_list);
+
+// Clean-up
+delete globalThis.eval_list;

test/fixtures/es-modules/module-cjs-deferred-eval.js

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+// This fixture is imported as a module
+// in test/es-module/test-cjs-defer-static-import-eval.mjs
+// to ensure a CommonJS module imported with `import defer`
+// is only executed once.
+const assert = require('assert');
+
+const identifier = 'package-type-commonjs';
+
+module.exports.foo = 42;
+module.exports.identifier = identifier;
+
+// The `eval_list` is initialised by the importing module,
+// so by the time the fixture is executed, `eval_list` should
+// already be initialised.
+assert.deepEqual(globalThis.eval_list, []);
+
+globalThis.eval_list.push('defer-1');