A new tui API for simple line editing

Handles basic line-editing with the extended keyboard protocol and
support for wide chars.
Currently used by the unicode input kitten.

kitty_tests/tui.py

@@ -0,0 +1,44 @@
+#!/usr/bin/env python
+# vim:fileencoding=utf-8
+# License: GPL v3 Copyright: 2018, Kovid Goyal <kovid at kovidgoyal.net>
+
+
+from . import BaseTest
+
+
+class TestTUI(BaseTest):
+
+    def test_line_edit(self):
+        from kittens.tui.line_edit import LineEdit
+        le = LineEdit()
+        le.on_text('abcd', False)
+        self.ae(le.cursor_pos, 4)
+        for i in range(5):
+            self.assertTrue(le.left()) if i < 4 else self.assertFalse(le.left())
+            self.ae(le.cursor_pos, max(0, 3 - i))
+        self.ae(le.pending_bell, True)
+        le.clear()
+        le.on_text('abcd', False), le.home()
+        self.ae(le.cursor_pos, 0)
+        for i in range(5):
+            self.assertTrue(le.right()) if i < 4 else self.assertFalse(le.right())
+            self.ae(le.cursor_pos, min(4, i + 1))
+        self.ae(le.pending_bell, True)
+        le.clear()
+        le.on_text('abcd', False)
+        self.ae(le.current_input, 'abcd')
+        self.ae(le.cursor_pos, 4)
+        self.ae(le.split_at_cursor(), ('abcd', ''))
+        le.backspace()
+        self.ae(le.current_input, 'abc')
+        self.ae(le.cursor_pos, 3)
+        self.assertFalse(le.pending_bell)
+        le.backspace(num=2)
+        self.ae(le.current_input, 'a')
+        self.ae(le.cursor_pos, 1)
+        self.assertFalse(le.pending_bell)
+        le.backspace(num=2)
+        self.ae(le.current_input, '')
+        self.ae(le.cursor_pos, 0)
+        le.backspace()
+        self.assertTrue(le.pending_bell)