Add additional test

Author: andyjansson

src/__tests__/index.js

@@ -42,6 +42,13 @@ test(
   '1ex'
 )
 
+test(
+  'should reduce simple calc (5)',
+  testFixture,
+  'calc(50px - (20px - 30px))',
+  '60px'
+)
+
 test(
   'should reduce additions and subtractions (1)',
   testFixture,