Testcase for symmetric extrusion

Added a test case for symmetric extrusion operation.

tests/TestCadQuery.py

@@ -1387,3 +1387,27 @@ class TestCadQuery(BaseTest):
         result =topOfLid.union(bottom)
 
         self.saveModel(result)
+        
+    def testExtrude(self):
+        """
+        Test symmetric extrude
+        """
+        r = 1.
+        h = 1.
+        decimal_places = 9.
+        
+        #extrude symmetrically
+        s = Workplane("XY").circle(r).extrude(h,both=True)
+        
+        top_face = s.faces(">Z")
+        bottom_face = s.faces("<Z")
+        
+        #calculate the distance between the top and the bottom face        
+        delta = top_face.val().Center().sub(bottom_face.val().Center())
+
+        self.assertTupleAlmostEquals(delta.toTuple(),
+                                     (0.,0.,2.*h),
+                                     decimal_places)
+        
+        
+