test: add smoke tests for defer importing synthetic modules

test/es-module/test-defer-import-builtin-module.mjs

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+// Flags: --js-defer-import-eval --experimental-import-text
+
+// Test that uses import.defer for a builtin module. Currently
+// defer importing of a synthetic module should be a no-op
+// in Node.js, so the test is mostly a smoke test that Node
+// doesn't crash.
+
+import '../common/index.mjs';
+import * as assert from 'assert';
+
+// Import the file system builtin module.
+import defer * as fs from 'node:fs';
+
+// Check that the imported module contains some known properties.
+assert.notStrictEqual(fs.constants, undefined);
+assert.notStrictEqual(fs.access, undefined);
+assert.strictEqual(typeof fs.access, 'function');
+
+// Check that the builtin module also exports some
+// usable contructor functions.
+assert.strictEqual(typeof fs.Stats, 'function');
+assert.strictEqual(typeof new fs.Stats(), 'object');

test/es-module/test-defer-import-json-module.mjs

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+// Flags: --js-defer-import-eval
+
+// Test that uses import.defer for a JSON module. Currently
+// defer importing of a synthetic module should be a no-op
+// in Node.js, so the test is mostly a smoke test that Node
+// doesn't crash.
+
+import '../common/index.mjs';
+import * as assert from 'assert';
+
+import defer * as imported_json
+  from '../fixtures/json-with-directory-name-module/module-stub.json'
+  with { type: 'json' };
+
+// Check that the imported object has the expected key/value.
+assert.strictEqual(imported_json.default.rocko, 'artischocko');

test/es-module/test-defer-import-text-module.mjs

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+// Flags: --js-defer-import-eval --experimental-import-text
+
+// Test that uses import.defer for a text module. Currently
+// defer importing of a synthetic module should be a no-op
+// in Node.js, so the test is mostly a smoke test that Node
+// doesn't crash.
+
+import '../common/index.mjs';
+import * as assert from 'assert';
+
+import defer * as imported_text
+  from '../fixtures/file-to-read-without-bom.txt'
+  with { type: 'text' };
+
+const expected_text = 'abc\ndef\nghi\n';
+
+// Check that the imported text has the expected value.
+assert.strictEqual(imported_text.default, expected_text);