Use a fake pad to make tests runnable

dungeonbattle/tests/screen.py

@@ -0,0 +1,14 @@
+class FakePad:
+    """
+    In order to run tests, we simulate a fake curses pad that accepts functions
+    but does nothing with them.
+    """
+    def addstr(self, y: int, x: int, message: str) -> None:
+        pass
+
+    def refresh(self, pminrow: int, pmincol: int, sminrow: int,
+                smincol: int, smaxrow: int, smaxcol: int) -> None:
+        pass
+
+    def clear(self):
+        pass