diff.diff

diff --git a/tests/test_core.py b/tests/test_core.py
index 0cf3327..c43e5ab 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -5574,6 +5574,31 @@ PORT: 3979
     self.emcc_args += ['--js-library', path_from_root('tests', 'unicode_library.js')]
     self.do_run(open(os.path.join(self.get_dir(), 'main.cpp'), 'r').read(), u'Unicode snowman \u2603 says hello!')
 
+  def test_js_library_features(self):
+    open(os.path.join(self.get_dir(), 'main.cpp'), 'w').write(r'''
+      #include <stdio.h>
+      extern "C" {
+        extern int countey();
+      }
+      int main() {
+        printf("%d\n", countey());
+        printf("%d\n", countey());
+        printf("%d\n", countey());
+        printf("%d\n", countey());
+        printf("%d\n", countey());
+        return 0;
+      }
+    ''')
+    open(os.path.join(self.get_dir(), 'mylib.js'), 'w').write('''
+      mergeInto(LibraryManager.library, {
+        // code provided in a string is emitted directly; this lets us do a closure in a simple way
+        countey: '(function() { var counter = 0; return function() { return counter++ }; })()',
+      });
+    ''')
+
+    self.emcc_args += ['--js-library', os.path.join(self.get_dir(), 'mylib.js')]
+    self.do_run(open(os.path.join(self.get_dir(), 'main.cpp'), 'r').read(), '0\n1\n2\n3\n4\n')
+
   def test_constglobalunion(self):
     self.emcc_args += ['-s', 'EXPORT_ALL=1']