Polygon more constructor tests

Add tests for the various times polygons should raise an exception.

* pygorithm/geometry/polygon2.py - minor documentation changes
* tests/test_geometry.py - more polygon constructor tests

Author: Tjstretchalot

pygorithm/geometry/polygon2.py

@@ -37,8 +37,8 @@ class Polygon2(object):
 
     .. caution::
         
-        The normals in the :py:attr:`~pygorithm.geometry.polygon2.Polygon2.normals`
-        are not necessarily the same length as 
+        The length of :py:attr:`~pygorithm.geometry.polygon2.Polygon2.normals`
+        is not necessarily the same as 
         :py:attr:`~pygorithm.geometry.polygon2.Polygon2.points` or 
         :py:attr:`~pygorithm.geometry.polygon2.Polygon2.lines`. It is only 
         guarranteed to have no two vectors that are the same or opposite 

tests/test_geometry.py

@@ -581,7 +581,22 @@ def test_constructor_standard(self):
 
         with self.assertRaises(StopIteration):
             next(i for i in range(4) if poly.points[i].x != poly2.points[i].x or poly.points[i].y != poly2.points[i].y)
+    
+    def test_constructor_repeated(self):
+        with self.assertRaises(ValueError):
+            poly = polygon2.Polygon2([ (0, 1), (1, 1), (1, 0), (0, 0), (0, 1) ])
+    
+    def test_constructor_two_points(self):
+        with self.assertRaises(ValueError):
+            poly = polygon2.Polygon2([ (0, 1), (1, 1) ])
 
+    def test_constructor_not_convex(self):
+        with self.assertRaises(ValueError):
+            poly = polygon2.Polygon2([ (0, 1), (0.5, 0.8), (1, 1), (1, 0), (0, 0) ])
+    
+    def test_cosntructor_not_clockwise(self):
+        with self.assertRaises(ValueError):
+            poly = polygon2.Polygon2([ (0, 0), (1, 0), (1, 1), (0, 1) ])
 
     def test_from_regular(self):
         diamond = polygon2.Polygon2.from_regular(4, 1)