test: add case for unrecognised fields within pjson "exports"

PR-URL: https://github.com/nodejs/node/pull/57026
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/fixtures/packages/unrecognised-export-keys/package.json

@@ -0,0 +1,10 @@
+{
+  "name": "pkg-with-unrecognised-export-keys",
+  "exports": {
+    ".": {
+      "default": "./index.js",
+      "FtLcAG": "./whatever.ext",
+      "types": "./index.d.ts"
+    }
+  }
+}

test/parallel/test-find-package-json.js

@@ -189,4 +189,19 @@ describe('findPackageJSON', () => { // Throws when no arguments are provided
     assert.ok(stdout.includes(foundPjsonPath), stdout);
     assert.strictEqual(code, 0);
   });
+
+  it('should work when unrecognised keys are specified within the export', async () => {
+    const specifierBase = './packages/unrecognised-export-keys';
+    const target = fixtures.fileURL(specifierBase, 'index.js');
+    const foundPjsonPath = path.toNamespacedPath(fixtures.path(specifierBase, 'package.json'));
+
+    const { code, stderr, stdout } = await common.spawnPromisified(process.execPath, [
+      '--print',
+      `require("node:module").findPackageJSON(${JSON.stringify(target)})`,
+    ]);
+
+    assert.strictEqual(stderr, '');
+    assert.ok(stdout.includes(foundPjsonPath), stdout);
+    assert.strictEqual(code, 0);
+  });
 });