add extra undo test

test/src/test_Buffer.cc

@@ -437,3 +437,25 @@ TEST(BufferTest, non_adjacent_erases_create_a_single_change_operation)
     b.undo();
     EXPECT_EQ(ss("abc\n"), b.get_string());
 }
+
+TEST(BufferTest, inserting_at_beginning_and_end_of_line_in_insert_mode_creates_proper_undo_operation)
+{
+    std::string s("abc\ndef\n");
+    Buffer b((const uint8_t *)&s[0], s.size());
+    auto it = b.add_cursor();
+
+    b.enter_insert_mode();
+    b.insert_code_point(*it, C('1'));
+    b.insert_code_point(*it, C('2'));
+    it->go_end_of_line(true);
+    b.insert_code_point(*it, C('3'));
+    b.insert_code_point(*it, C('4'));
+    b.exit_insert_mode();
+    EXPECT_EQ("12abc34\ndef\n", b.get_string());
+
+    b.undo();
+    EXPECT_EQ("abc\ndef\n", b.get_string());
+
+    b.redo();
+    EXPECT_EQ("12abc34\ndef\n", b.get_string());
+}