diff --git a/lib/reline/general_io.rb b/lib/reline/general_io.rb
index eaae63f925..b830eb39a0 100644
--- a/lib/reline/general_io.rb
+++ b/lib/reline/general_io.rb
@@ -57,7 +57,7 @@ def self.ungetc(c)
   end
 
   def self.get_screen_size
-    [1, 1]
+    [24, 80]
   end
 
   def self.cursor_pos
diff --git a/test/reline/helper.rb b/test/reline/helper.rb
index fb2262e7f5..2180fdf596 100644
--- a/test/reline/helper.rb
+++ b/test/reline/helper.rb
@@ -29,12 +29,19 @@ def test_mode(ansi: false)
       else
         encoding = Encoding::UTF_8
       end
+      @original_get_screen_size = IOGate.method(:get_screen_size)
+      IOGate.singleton_class.remove_method(:get_screen_size)
+      def IOGate.get_screen_size
+        [24, 80]
+      end
       Reline::GeneralIO.reset(encoding: encoding) unless ansi
       core.config.instance_variable_set(:@test_mode, true)
       core.config.reset
     end
 
     def test_reset
+      IOGate.singleton_class.remove_method(:get_screen_size)
+      IOGate.define_singleton_method(:get_screen_size, @original_get_screen_size)
       remove_const('IOGate')
       const_set('IOGate', @original_iogate)
       Reline::GeneralIO.reset
@@ -147,11 +154,22 @@ def assert_byte_pointer_size(expected)
   end
 
   def assert_cursor(expected)
-    assert_equal(expected, @line_editor.instance_variable_get(:@cursor))
+    # This test satisfies nothing because there is no `@cursor` anymore
+    # Test editor_cursor_position instead
+    cursor_x = @line_editor.instance_eval do
+      line_before_cursor = whole_lines[@line_index].byteslice(0, @byte_pointer)
+      Reline::Unicode.calculate_width(line_before_cursor)
+    end
+    assert_equal(expected, cursor_x)
   end
 
   def assert_cursor_max(expected)
-    assert_equal(expected, @line_editor.instance_variable_get(:@cursor_max))
+    # This test satisfies nothing because there is no `@cursor_max` anymore
+    cursor_max = @line_editor.instance_eval do
+      line = whole_lines[@line_index]
+      Reline::Unicode.calculate_width(line)
+    end
+    assert_equal(expected, cursor_max)
   end
 
   def assert_line_index(expected)
diff --git a/test/reline/test_key_actor_emacs.rb b/test/reline/test_key_actor_emacs.rb
index 4575e51eb2..d5ddd40f85 100644
--- a/test/reline/test_key_actor_emacs.rb
+++ b/test/reline/test_key_actor_emacs.rb
@@ -1737,19 +1737,19 @@ def test_search_history_to_back
     assert_cursor_max(0)
     input_keys("\C-r123")
     assert_line('1234')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0) # doesn't determine yet
+    assert_byte_pointer_size('1234')
+    assert_cursor(4)
+    assert_cursor_max(4)
     input_keys("\C-ha")
     assert_line('12aa')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0)
+    assert_byte_pointer_size('12aa')
+    assert_cursor(4)
+    assert_cursor_max(4)
     input_keys("\C-h3")
     assert_line('1235')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0)
+    assert_byte_pointer_size('1235')
+    assert_cursor(4)
+    assert_cursor_max(4)
   end
 
   def test_search_history_to_front
@@ -1764,19 +1764,19 @@ def test_search_history_to_front
     assert_cursor_max(0)
     input_keys("\C-s123")
     assert_line('1235')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0) # doesn't determine yet
+    assert_byte_pointer_size('1235')
+    assert_cursor(4)
+    assert_cursor_max(4)
     input_keys("\C-ha")
     assert_line('12aa')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0)
+    assert_byte_pointer_size('12aa')
+    assert_cursor(4)
+    assert_cursor_max(4)
     input_keys("\C-h3")
     assert_line('1234')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0)
+    assert_byte_pointer_size('1234')
+    assert_cursor(4)
+    assert_cursor_max(4)
   end
 
   def test_search_history_front_and_back
@@ -1791,24 +1791,24 @@ def test_search_history_front_and_back
     assert_cursor_max(0)
     input_keys("\C-s12")
     assert_line('1235')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0) # doesn't determine yet
+    assert_byte_pointer_size('1235')
+    assert_cursor(4)
+    assert_cursor_max(4)
     input_keys("\C-s")
     assert_line('12aa')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0)
+    assert_byte_pointer_size('12aa')
+    assert_cursor(4)
+    assert_cursor_max(4)
     input_keys("\C-r")
     assert_line('12aa')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0)
+    assert_byte_pointer_size('12aa')
+    assert_cursor(4)
+    assert_cursor_max(4)
     input_keys("\C-r")
     assert_line('1235')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0)
+    assert_byte_pointer_size('1235')
+    assert_cursor(4)
+    assert_cursor_max(4)
   end
 
   def test_search_history_back_and_front
@@ -1823,24 +1823,24 @@ def test_search_history_back_and_front
     assert_cursor_max(0)
     input_keys("\C-r12")
     assert_line('1234')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0) # doesn't determine yet
+    assert_byte_pointer_size('1234')
+    assert_cursor(4)
+    assert_cursor_max(4)
     input_keys("\C-r")
     assert_line('12aa')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0)
+    assert_byte_pointer_size('12aa')
+    assert_cursor(4)
+    assert_cursor_max(4)
     input_keys("\C-s")
     assert_line('12aa')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0)
+    assert_byte_pointer_size('12aa')
+    assert_cursor(4)
+    assert_cursor_max(4)
     input_keys("\C-s")
     assert_line('1234')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0)
+    assert_byte_pointer_size('1234')
+    assert_cursor(4)
+    assert_cursor_max(4)
   end
 
   def test_search_history_to_back_in_the_middle_of_histories
@@ -1877,14 +1877,14 @@ def test_search_history_twice
     assert_cursor_max(0)
     input_keys("\C-r123")
     assert_line('1234')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0) # doesn't determine yet
+    assert_byte_pointer_size('1234')
+    assert_cursor(4)
+    assert_cursor_max(4)
     input_keys("\C-r")
     assert_line('1235')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0)
+    assert_byte_pointer_size('1235')
+    assert_cursor(4)
+    assert_cursor_max(4)
   end
 
   def test_search_history_by_last_determined
@@ -1899,9 +1899,9 @@ def test_search_history_by_last_determined
     assert_cursor_max(0)
     input_keys("\C-r123")
     assert_line('1234')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0) # doesn't determine yet
+    assert_byte_pointer_size('1234')
+    assert_cursor(4)
+    assert_cursor_max(4)
     input_keys("\C-j")
     assert_line('1234')
     assert_byte_pointer_size('')
@@ -1919,9 +1919,9 @@ def test_search_history_by_last_determined
     assert_cursor_max(0)
     input_keys("\C-r")
     assert_line('1235')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0)
+    assert_byte_pointer_size('1235')
+    assert_cursor(4)
+    assert_cursor_max(4)
   end
 
   def test_search_history_with_isearch_terminator
@@ -1939,9 +1939,9 @@ def test_search_history_with_isearch_terminator
     assert_cursor_max(0)
     input_keys("\C-r12a")
     assert_line('12aa')
-    assert_byte_pointer_size('')
-    assert_cursor(0)
-    assert_cursor_max(0) # doesn't determine yet
+    assert_byte_pointer_size('12aa')
+    assert_cursor(4)
+    assert_cursor_max(4)
     input_keys('Y')
     assert_line('12aa')
     assert_byte_pointer_size('')
@@ -2013,7 +2013,7 @@ def test_modify_lines_with_wrong_rs
     $VERBOSE = verbose
     @line_editor.output_modifier_proc = proc { |output| Reline::Unicode.escape_for_print(output) }
     input_keys("abcdef\n")
-    result = @line_editor.__send__(:modify_lines, @line_editor.whole_lines)
+    result = @line_editor.__send__(:modify_lines, @line_editor.whole_lines, @line_editor.finished?)
     $/ = nil
     assert_equal(['abcdef'], result)
   ensure
diff --git a/test/reline/test_line_editor.rb b/test/reline/test_line_editor.rb
index 8399e76e92..a5fcc3e2a1 100644
--- a/test/reline/test_line_editor.rb
+++ b/test/reline/test_line_editor.rb
@@ -1,13 +1,124 @@
 require_relative 'helper'
 require 'reline/line_editor'
+require 'stringio'
 
-class Reline::LineEditor::Test < Reline::TestCase
-  def test_range_subtract
-    dummy_config = nil
-    editor = Reline::LineEditor.new(dummy_config, 'ascii-8bit')
-    base_ranges = [3...5, 4...10, 6...8, 12...15, 15...20]
-    subtract_ranges = [5...7, 8...9, 11...13, 17...18, 18...19]
-    expected_result = [3...5, 7...8, 9...10, 13...17, 19...20]
-    assert_equal expected_result, editor.send(:range_subtract, base_ranges, subtract_ranges)
+class Reline::LineEditor
+  class RenderLineDifferentialTest < Reline::TestCase
+    def setup
+      verbose, $VERBOSE = $VERBOSE, nil
+      @line_editor = Reline::LineEditor.new(nil, Encoding::UTF_8)
+      @original_iogate = Reline::IOGate
+      @output = StringIO.new
+      @line_editor.instance_variable_set(:@screen_size, [24, 80])
+      @line_editor.instance_variable_set(:@output, @output)
+      Reline.send(:remove_const, :IOGate)
+      Reline.const_set(:IOGate, Object.new)
+      Reline::IOGate.instance_variable_set(:@output, @output)
+      def (Reline::IOGate).move_cursor_column(col)
+        @output << "[COL_#{col}]"
+      end
+      def (Reline::IOGate).erase_after_cursor
+        @output << '[ERASE]'
+      end
+    ensure
+      $VERBOSE = verbose
+    end
+
+    def assert_output(expected)
+      @output.reopen('')
+      yield
+      actual = @output.string
+      assert_equal(expected, actual.gsub("\e[0m", ''))
+    end
+
+    def teardown
+      Reline.send(:remove_const, :IOGate)
+      Reline.const_set(:IOGate, @original_iogate)
+    end
+
+    def test_line_increase_decrease
+      assert_output '[COL_0]bb' do
+        @line_editor.render_line_differential([[0, 1, 'a']], [[0, 2, 'bb']])
+      end
+
+      assert_output '[COL_0]b[COL_1][ERASE]' do
+        @line_editor.render_line_differential([[0, 2, 'aa']], [[0, 1, 'b']])
+      end
+    end
+
+    def test_dialog_apear_disappear
+      assert_output '[COL_3]dialog' do
+        @line_editor.render_line_differential([[0, 1, 'a']], [[0, 1, 'a'], [3, 6, 'dialog']])
+      end
+
+      assert_output '[COL_3]dialog' do
+        @line_editor.render_line_differential([[0, 10, 'a' * 10]], [[0, 10, 'a' * 10], [3, 6, 'dialog']])
+      end
+
+      assert_output '[COL_1][ERASE]' do
+        @line_editor.render_line_differential([[0, 1, 'a'], [3, 6, 'dialog']], [[0, 1, 'a']])
+      end
+
+      assert_output '[COL_3]aaaaaa' do
+        @line_editor.render_line_differential([[0, 10, 'a' * 10], [3, 6, 'dialog']], [[0, 10, 'a' * 10]])
+      end
+    end
+
+    def test_dialog_change
+      assert_output '[COL_3]DIALOG' do
+        @line_editor.render_line_differential([[0, 2, 'a'], [3, 6, 'dialog']], [[0, 2, 'a'], [3, 6, 'DIALOG']])
+      end
+
+      assert_output '[COL_3]DIALOG' do
+        @line_editor.render_line_differential([[0, 10, 'a' * 10], [3, 6, 'dialog']], [[0, 10, 'a' * 10], [3, 6, 'DIALOG']])
+      end
+    end
+
+    def test_update_under_dialog
+      assert_output '[COL_0]b[COL_1] ' do
+        @line_editor.render_line_differential([[0, 2, 'aa'], [4, 6, 'dialog']], [[0, 1, 'b'], [4, 6, 'dialog']])
+      end
+
+      assert_output '[COL_0]bbb[COL_9]b' do
+        @line_editor.render_line_differential([[0, 10, 'a' * 10], [3, 6, 'dialog']], [[0, 10, 'b' * 10], [3, 6, 'dialog']])
+      end
+
+      assert_output '[COL_0]b[COL_1]  [COL_9][ERASE]' do
+        @line_editor.render_line_differential([[0, 10, 'a' * 10], [3, 6, 'dialog']], [[0, 1, 'b'], [3, 6, 'dialog']])
+      end
+    end
+
+    def test_dialog_move
+      assert_output '[COL_3]dialog[COL_9][ERASE]' do
+        @line_editor.render_line_differential([[0, 1, 'a'], [4, 6, 'dialog']], [[0, 1, 'a'], [3, 6, 'dialog']])
+      end
+
+      assert_output '[COL_4] [COL_5]dialog' do
+        @line_editor.render_line_differential([[0, 1, 'a'], [4, 6, 'dialog']], [[0, 1, 'a'], [5, 6, 'dialog']])
+      end
+
+      assert_output '[COL_2]dialog[COL_8]a' do
+        @line_editor.render_line_differential([[0, 10, 'a' * 10], [3, 6, 'dialog']], [[0, 10, 'a' * 10], [2, 6, 'dialog']])
+      end
+
+      assert_output '[COL_2]a[COL_3]dialog' do
+        @line_editor.render_line_differential([[0, 10, 'a' * 10], [2, 6, 'dialog']], [[0, 10, 'a' * 10], [3, 6, 'dialog']])
+      end
+    end
+
+    def test_complex
+      state_a = [nil, [19, 7, 'bbbbbbb'], [15, 8, 'cccccccc'], [10, 5, 'ddddd'], [18, 4, 'eeee'], [1, 3, 'fff'], [17, 2, 'gg'], [7, 1, 'h']]
+      state_b = [[5, 9, 'aaaaaaaaa'], nil, [15, 8, 'cccccccc'], nil, [18, 4, 'EEEE'], [25, 4, 'ffff'], [17, 2, 'gg'], [2, 2, 'hh']]
+      # state_a: " fff   h  dddddccggeeecbbb"
+      # state_b: "  hh aaaaaaaaa ccggEEEc  ffff"
+
+      assert_output '[COL_1] [COL_2]hh[COL_5]aaaaaaaaa[COL_14] [COL_19]EEE[COL_23]  [COL_25]ffff' do
+        @line_editor.render_line_differential(state_a, state_b)
+      end
+
+      assert_output '[COL_1]fff[COL_5]  [COL_7]h[COL_8]  [COL_10]ddddd[COL_19]eee[COL_23]bbb[COL_26][ERASE]' do
+        @line_editor.render_line_differential(state_b, state_a)
+      end
+    end
   end
 end
diff --git a/test/reline/test_macro.rb b/test/reline/test_macro.rb
index 3096930830..04aa6474b4 100644
--- a/test/reline/test_macro.rb
+++ b/test/reline/test_macro.rb
@@ -6,7 +6,6 @@ def setup
     @config = Reline::Config.new
     @encoding = Reline.core.encoding
     @line_editor = Reline::LineEditor.new(@config, @encoding)
-    @line_editor.instance_variable_set(:@screen_size, [24, 80])
     @output = @line_editor.output = File.open(IO::NULL, "w")
   end
 
diff --git a/test/reline/yamatanooroti/test_rendering.rb b/test/reline/yamatanooroti/test_rendering.rb
index b61c84527d..3b1f63adff 100644
--- a/test/reline/yamatanooroti/test_rendering.rb
+++ b/test/reline/yamatanooroti/test_rendering.rb
@@ -464,6 +464,9 @@ def test_multiline_incremental_search
       write("def a\n  8\nend\ndef b\n  3\nend\C-s8")
       close
       assert_screen(<<~EOC)
+        prompt>   8
+        prompt> end
+        => :a
         (i-search)`8'def a
         (i-search)`8'  8
         (i-search)`8'end
@@ -475,6 +478,9 @@ def test_multiline_incremental_search_finish
       write("def a\n  8\nend\ndef b\n  3\nend\C-r8\C-j")
       close
       assert_screen(<<~EOC)
+        prompt>   8
+        prompt> end
+        => :a
         prompt> def a
         prompt>   8
         prompt> end
@@ -1026,8 +1032,8 @@ def test_dialog_scroll_pushup_condition
       iterate_over_face_configs do |config_name, config_file|
         start_terminal(10, 50, %W{ruby -I#{@pwd}/lib -r#{config_file.path} #{@pwd}/test/reline/yamatanooroti/multiline_repl --autocomplete}, startup_message: 'Multiline REPL.')
         write("\n" * 10)
-        write("if 1\n  sSt\nend")
-        write("\C-p\C-h\C-e")
+        write("if 1\n  sSts\nend")
+        write("\C-p\C-h\C-e\C-h")
         close
         assert_screen(<<~'EOC')
           prompt>
@@ -1054,8 +1060,8 @@ def test_simple_dialog_with_scroll_screen
           prompt>   2
           prompt>   3#
           prompt>   4
-          prompt>   5
-          prompt>   6 Ruby is...
+          prompt>   5 Ruby is...
+          prompt>   6 A dynamic, open source programming
         EOC
       end
     end