old_contents: # Licensed to CRATE Technology GmbH ("Crate") under one or more contributor
  # license agreements.  See the NOTICE file distributed with this work for
  # additional information regarding copyright ownership.  Crate licenses
  # this file to you under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.  You may
  # obtain a copy of the License at
  #
  #   http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
  # License for the specific language governing permissions and limitations
  # under the License.
  #
  # However, if you have executed another commercial license agreement
  # with Crate these terms will supersede the license and you may use the
  # software solely pursuant to the terms of the relevant commercial agreement.
  
  from unittest import TestCase
  from prompt_toolkit.document import Document
  from .keybinding import _is_start_of_multiline, _line_ends_with_tab
  
  
  doc = lambda t: Document(t, len(t))
  is_start_of_multiline = lambda t: _is_start_of_multiline(doc(t))
  line_ends_with_tab = lambda t: _line_ends_with_tab(doc(t))
  
  
  class TabIndentTest(TestCase):
  
      def test_indent(self):
          self.assertFalse(is_start_of_multiline(''))
          self.assertFalse(is_start_of_multiline('SELECT'))
          self.assertFalse(is_start_of_multiline('SELECT\n*'))
          self.assertTrue(is_start_of_multiline('SELECT\n'))
          self.assertTrue(is_start_of_multiline('SELECT\n '))
          self.assertTrue(is_start_of_multiline('\n'))
  
      def test_deindent(self):
          self.assertFalse(line_ends_with_tab(''))
          self.assertFalse(line_ends_with_tab('SELECT'))
          self.assertFalse(line_ends_with_tab('SELECT  '))
          self.assertFalse(line_ends_with_tab('SELECT  \n'))
          self.assertTrue(line_ends_with_tab('SELECT    '))
          self.assertTrue(line_ends_with_tab('SELECT\n    '))
  
new_contents: # Licensed to CRATE Technology GmbH ("Crate") under one or more contributor
  # license agreements.  See the NOTICE file distributed with this work for
  # additional information regarding copyright ownership.  Crate licenses
  # this file to you under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.  You may
  # obtain a copy of the License at
  #
  #   http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
  # License for the specific language governing permissions and limitations
  # under the License.
  #
  # However, if you have executed another commercial license agreement
  # with Crate these terms will supersede the license and you may use the
  # software solely pursuant to the terms of the relevant commercial agreement.
  
  from unittest import TestCase
  from prompt_toolkit.document import Document
  from prompt_toolkit.keys import Keys
  from prompt_toolkit.key_binding.manager import KeyBindingManager
  from .keybinding import bind_keys, _is_start_of_multiline, _line_ends_with_tab
  
  
  doc = lambda t: Document(t, len(t))
  is_start_of_multiline = lambda t: _is_start_of_multiline(doc(t))
  line_ends_with_tab = lambda t: _line_ends_with_tab(doc(t))
  
  
  def bindings_for_key(mngr, key):
      return mngr.registry.get_bindings_for_keys((key,))
  
  
  def handlers_for_key(mngr, key):
      return [b.handler.__name__ for b in bindings_for_key(mngr, key)]
  
  
  class TabIndentTest(TestCase):
  
      def test_indent(self):
          self.assertFalse(is_start_of_multiline(''))
          self.assertFalse(is_start_of_multiline('SELECT'))
          self.assertFalse(is_start_of_multiline('SELECT\n*'))
          self.assertTrue(is_start_of_multiline('SELECT\n'))
          self.assertTrue(is_start_of_multiline('SELECT\n '))
          self.assertTrue(is_start_of_multiline('\n'))
  
      def test_deindent(self):
          self.assertFalse(line_ends_with_tab(''))
          self.assertFalse(line_ends_with_tab('SELECT'))
          self.assertFalse(line_ends_with_tab('SELECT  '))
          self.assertFalse(line_ends_with_tab('SELECT  \n'))
          self.assertTrue(line_ends_with_tab('SELECT    '))
          self.assertTrue(line_ends_with_tab('SELECT\n    '))
  
      def test_bindings(self):
          mngr = KeyBindingManager(
              enable_search=True,
              enable_abort_and_exit_bindings=True,
              enable_system_bindings=True,
              enable_open_in_editor=True
          )
          bind_keys(mngr.registry)
  
          self.assertTrue('on_backspace' in handlers_for_key(mngr, Keys.Backspace))
          self.assertTrue('on_tab' in handlers_for_key(mngr, Keys.Tab))
  
subject: add test for <BACKSPACE> binding to delete 4 spaces