1 files changed, 151 insertions, 0 deletions
diff --git a/helix-tui/src/backend/test.rs b/helix-tui/src/backend/test.rs
new file mode 100644
index 00000000..46b37261
--- /dev/null
+++ b/helix-tui/src/backend/test.rs
@@ -0,0 +1,151 @@
+use crate::{
+    backend::Backend,
+    buffer::{Buffer, Cell},
+    layout::Rect,
+};
+use std::{fmt::Write, io};
+use unicode_width::UnicodeWidthStr;
+
+/// A backend used for the integration tests.
+#[derive(Debug)]
+pub struct TestBackend {
+    width: u16,
+    buffer: Buffer,
+    height: u16,
+    cursor: bool,
+    pos: (u16, u16),
+}
+
+/// Returns a string representation of the given buffer for debugging purpose.
+fn buffer_view(buffer: &Buffer) -> String {
+    let mut view = String::with_capacity(buffer.content.len() + buffer.area.height as usize * 3);
+    for cells in buffer.content.chunks(buffer.area.width as usize) {
+        let mut overwritten = vec![];
+        let mut skip: usize = 0;
+        view.push('"');
+        for (x, c) in cells.iter().enumerate() {
+            if skip == 0 {
+                view.push_str(&c.symbol);
+            } else {
+                overwritten.push((x, &c.symbol))
+            }
+            skip = std::cmp::max(skip, c.symbol.width()).saturating_sub(1);
+        }
+        view.push('"');
+        if !overwritten.is_empty() {
+            write!(
+                &mut view,
+                " Hidden by multi-width symbols: {:?}",
+                overwritten
+            )
+            .unwrap();
+        }
+        view.push('\n');
+    }
+    view
+}
+
+impl TestBackend {
+    pub fn new(width: u16, height: u16) -> TestBackend {
+        TestBackend {
+            width,
+            height,
+            buffer: Buffer::empty(Rect::new(0, 0, width, height)),
+            cursor: false,
+            pos: (0, 0),
+        }
+    }
+
+    pub fn buffer(&self) -> &Buffer {
+        &self.buffer
+    }
+
+    pub fn resize(&mut self, width: u16, height: u16) {
+        self.buffer.resize(Rect::new(0, 0, width, height));
+        self.width = width;
+        self.height = height;
+    }
+
+    pub fn assert_buffer(&self, expected: &Buffer) {
+        assert_eq!(expected.area, self.buffer.area);
+        let diff = expected.diff(&self.buffer);
+        if diff.is_empty() {
+            return;
+        }
+
+        let mut debug_info = String::from("Buffers are not equal");
+        debug_info.push('\n');
+        debug_info.push_str("Expected:");
+        debug_info.push('\n');
+        let expected_view = buffer_view(expected);
+        debug_info.push_str(&expected_view);
+        debug_info.push('\n');
+        debug_info.push_str("Got:");
+        debug_info.push('\n');
+        let view = buffer_view(&self.buffer);
+        debug_info.push_str(&view);
+        debug_info.push('\n');
+
+        debug_info.push_str("Diff:");
+        debug_info.push('\n');
+        let nice_diff = diff
+            .iter()
+            .enumerate()
+            .map(|(i, (x, y, cell))| {
+                let expected_cell = expected.get(*x, *y);
+                format!(
+                    "{}: at ({}, {}) expected {:?} got {:?}",
+                    i, x, y, expected_cell, cell
+                )
+            })
+            .collect::<Vec<String>>()
+            .join("\n");
+        debug_info.push_str(&nice_diff);
+        panic!("{}", debug_info);
+    }
+}
+
+impl Backend for TestBackend {
+    fn draw<'a, I>(&mut self, content: I) -> Result<(), io::Error>
+    where
+        I: Iterator<Item = (u16, u16, &'a Cell)>,
+    {
+        for (x, y, c) in content {
+            let cell = self.buffer.get_mut(x, y);
+            *cell = c.clone();
+        }
+        Ok(())
+    }
+
+    fn hide_cursor(&mut self) -> Result<(), io::Error> {
+        self.cursor = false;
+        Ok(())
+    }
+
+    fn show_cursor(&mut self) -> Result<(), io::Error> {
+        self.cursor = true;
+        Ok(())
+    }
+
+    fn get_cursor(&mut self) -> Result<(u16, u16), io::Error> {
+        Ok(self.pos)
+    }
+
+    fn set_cursor(&mut self, x: u16, y: u16) -> Result<(), io::Error> {
+        self.pos = (x, y);
+        Ok(())
+    }
+
+    fn clear(&mut self) -> Result<(), io::Error> {
+        self.buffer.reset();
+        Ok(())
+    }
+
+    fn size(&self) -> Result<Rect, io::Error> {
+        Ok(Rect::new(0, 0, self.width, self.height))
+    }
+
+    fn flush(&mut self) -> Result<(), io::Error> {
+        Ok(())
+    }
+}