Make Buffer tests prettier with method chaining

Feel like I'm gonna regret this but YOLO.

editor/main.py

@@ -47,14 +47,19 @@ class Buffer:
         self.cx = cx
         self.cy = cy
 
-    def up(self) -> None:
-        self.cy -= 1
+    def up(self) -> "Buffer":
+        if self.cy > 0:
+            self.cy -= 1
+        return self
 
-    def down(self) -> None:
+    def down(self) -> "Buffer":
         self.cy += 1
+        return self
 
-    def left(self) -> None:
+    def left(self) -> "Buffer":
         self.cx -= 1
+        return self
 
-    def right(self) -> None:
+    def right(self) -> "Buffer":
         self.cx += 1
+        return self

tests/main_test.py

@@ -1,30 +1,25 @@
 from editor.main import Buffer
 
 
-def test_buffer_init():
-    buf = Buffer()
-    assert buf.cx == buf.cy == 0
-
-
 def test_buffer_up():
-    buf = Buffer(cy=1)
-    buf.up()
-    assert buf.cy == 0
+    assert Buffer(cy=1).up().cy == 0
+
+
+def test_buffer_up_at_first_line():
+    assert Buffer().up().cy == 0
 
 
 def test_buffer_down():
-    buf = Buffer()
-    buf.down()
-    assert buf.cy == 1
+    assert Buffer().down().cy == 1
+
+
+def test_buffer_down_at_last_line():
+    assert Buffer().up().cy == 0
 
 
 def test_buffer_left():
-    buf = Buffer(cx=1)
-    buf.left()
-    assert buf.cx == 0
+    assert Buffer(cx=1).left().cx == 0
 
 
 def test_buffer_right():
-    buf = Buffer()
-    buf.right()
-    assert buf.cx == 1
+    assert Buffer().right().cx == 1