You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: test.rs
    path of file: ./repos/ratatui/src/backend
    
    the code of the file until where you have to start completion: //! This module provides the `TestBackend` implementation for the [`Backend`] trait.
//! It is used in the integration tests to verify the correctness of the library.

use std::{
    fmt::{Display, Write},
    io,
};

use unicode_width::UnicodeWidthStr;

use crate::{
    assert_buffer_eq,
    backend::{Backend, ClearType, WindowSize},
    buffer::{Buffer, Cell},
    layout::{Rect, Size},
};

/// A [`Backend`] implementation used for integration testing that that renders to an in memory
/// buffer.
///
/// Note: that although many of the integration and unit tests in ratatui are written using this
/// backend, it is preferable to write unit tests for widgets directly against the buffer rather
/// than using this backend. This backend is intended for integration tests that test the entire
/// terminal UI.
///
/// # Example
///
/// ```rust
/// use ratatui::{backend::TestBackend, prelude::*};
///
/// let mut backend = TestBackend::new(10, 2);
/// backend.clear()?;
/// backend.assert_buffer(&Buffer::with_lines(vec!["          "; 2]));
/// # std::io::Re
    
    fn clear_region(&mut self, clear_type: super::ClearType) -> io::Result<()> {
        match clear_type {
            ClearType::All => self.clear()?,
            ClearType::AfterCursor => {
                let index = self.buffer.index_of(self.pos.0, self.pos.1) + 1;
                self.buffer.content[index..].fill(Cell::default());
            }
            ClearType::BeforeCursor => {
                let index = self.buffer.index_of(self.pos.0, self.pos.1);
                self.buffer.content[..index].fill(Cell::default());
            }
            ClearType::CurrentLine => {
                let line_start_index = self.buffer.index_of(0, self.pos.1);
                let line_end_index = self.buffer.index_of(self.width - 1, self.pos.1);
                self.buffer.content[line_start_index..=line_end_index].fill(Cell::default());
            }
            ClearType::UntilNewLine => {
                let index = self.buffer.index_of(self.pos.0, self.pos.1);
                let line_end_index = self.buffer.index_of(self.width - 1, self.pos.1);
                self.buffer.content[index..=line_end_index].fill(Cell::default());
            }
        }
        Ok(())
    }