diff --git a/test/env_fn.js b/test/env_fn.js
new file mode 100644
index 0000000..0762f2d
--- /dev/null
+++ b/test/env_fn.js
@@ -0,0 +1,17 @@
+var test = require('tape');
+var parse = require('../').parse;
+
+test('functional env expansion', function (t) {
+    t.plan(2);
+    
+    t.same(parse('a $XYZ c', getEnv), [ 'a', 'xxx', 'c' ]);
+    t.same(parse('a $XYZ c', getEnvObj), [ 'a', { op: '@@' }, 'c' ]);
+    
+    function getEnv (key) {
+        return 'xxx';
+    }
+    
+    function getEnvObj (key) {
+        return { op: '@@' };
+    }
+});