diff -r 8990ac138cc2 -r 7c263b864371 tests/quadrilaterals.py
--- a/tests/quadrilaterals.py	Mon Jan 22 21:04:53 2018 +0200
+++ b/tests/quadrilaterals.py	Mon Jan 22 21:21:53 2018 +0200
@@ -7,6 +7,7 @@
     return min(container) * max(container) >= 0
 
 def concave_test(model):
+    ''' Checks that all quadrilaterals are convex. '''
     for quadrilateral in model.quadrilaterals:
         geometry = transform_to_xy(quadrilateral.geometry)
         z_scores = [
@@ -17,7 +18,7 @@
             yield error(quadrilateral, 'concave-error')
 
 def skew_test(model):
-    ''' Test for non-coplanar quadrilaterals. '''
+    ''' Checks that all quadrilaterals are coplanar. '''
     for quadrilateral in model.quadrilaterals:
         for triangles in split_quadrilateral(quadrilateral.geometry):
             plane_1 = triangle_plane_normal(triangles[0])