Ensure tests pass

src/prompt_toolkit/border.py

@@ -1,7 +1,25 @@
 """Defines borders."""
 
+from abc import ABCMeta
 
-class SquareBorder:
+
+class Border(metaclass=ABCMeta):
+ """Base border type."""
+
+ TOP_LEFT: str
+ TOP_SPLIT: str
+ TOP_RIGHT: str
+ HORIZONTAL: str
+ VERTICAL: str
+ LEFT_SPLIT: str
+ RIGHT_SPLIT: str
+ CROSS: str
+ BOTTOM_LEFT: str
+ BOTTOM_SPLIT: str
+ BOTTOM_RIGHT: str
+
+
+class SquareBorder(Border):
  """Square thin border."""
 
  TOP_LEFT = "┌"
@@ -17,7 +35,7 @@ class SquareBorder:
  BOTTOM_RIGHT = "┘"
 
 
-class DoubleBorder:
+class DoubleBorder(Border):
  """Box drawing characters with double lines."""
 
  TOP_LEFT = "╔"