tests: improved testability

Cargo.lock

@@ -118,6 +118,7 @@ name = "chkr"
 version = "0.1.0"
 dependencies = [
  "crossterm",
+ "insta",
  "ratatui",
 ]
 
@@ -135,6 +136,18 @@ dependencies = [
  "static_assertions",
 ]
 
+[[package]]
+name = "console"
+version = "0.15.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "054ccb5b10f9f2cbf51eb355ca1d05c2d279ce1804688d0db74b4733a5aeafd8"
+dependencies = [
+ "encode_unicode",
+ "libc",
+ "once_cell",
+ "windows-sys 0.59.0",
+]
+
 [[package]]
 name = "convert_case"
 version = "0.10.0"
@@ -296,6 +309,12 @@ version = "1.15.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "48c757948c5ede0e46177b7add2e67155f70e33c07fea8284df6576da70b3719"
 
+[[package]]
+name = "encode_unicode"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "34aa73646ffb006b8f5147f3dc182bd4bcb190227ce861fc4a4844bf8e3cb2c0"
+
 [[package]]
 name = "equivalent"
 version = "1.0.2"
@@ -309,7 +328,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "39cab71617ae0d63f51a36d69f866391735b51691dbda63cf6f96d042b63efeb"
 dependencies = [
  "libc",
- "windows-sys",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -331,6 +350,12 @@ dependencies = [
  "regex",
 ]
 
+[[package]]
+name = "fastrand"
+version = "2.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "37909eebbb50d72f9059c3b6d82c0463f2ff062c9e95845c43a6c9c0355411be"
+
 [[package]]
 name = "filedescriptor"
 version = "0.8.3"
@@ -426,6 +451,18 @@ dependencies = [
  "rustversion",
 ]
 
+[[package]]
+name = "insta"
+version = "1.46.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "248b42847813a1550dafd15296fd9748c651d0c32194559dbc05d804d54b21e8"
+dependencies = [
+ "console",
+ "once_cell",
+ "similar",
+ "tempfile",
+]
+
 [[package]]
 name = "instability"
 version = "0.3.11"
@@ -584,7 +621,7 @@ dependencies = [
  "libc",
  "log",
  "wasi",
- "windows-sys",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -971,7 +1008,7 @@ dependencies = [
  "errno",
  "libc",
  "linux-raw-sys",
- "windows-sys",
+ "windows-sys 0.61.2",
 ]
 
 [[package]]
@@ -1070,6 +1107,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "similar"
+version = "2.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "bbbb5d9659141646ae647b42fe094daf6c6192d1620870b449d9557f748b2daa"
+
 [[package]]
 name = "siphasher"
 version = "1.0.1"
@@ -1137,6 +1180,19 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "tempfile"
+version = "3.24.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "655da9c7eb6305c55742045d5a8d2037996d61d8de95806335c7c86ce0f82e9c"
+dependencies = [
+ "fastrand",
+ "getrandom",
+ "once_cell",
+ "rustix",
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "terminfo"
 version = "0.9.0"
@@ -1495,6 +1551,15 @@ version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
 
+[[package]]
+name = "windows-sys"
+version = "0.59.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e38bc4d79ed67fd075bcc251a1c39b32a1776bbe92e5bef1f0bf1f8c531853b"
+dependencies = [
+ "windows-targets",
+]
+
 [[package]]
 name = "windows-sys"
 version = "0.61.2"
@@ -1504,6 +1569,70 @@ dependencies = [
  "windows-link",
 ]
 
+[[package]]
+name = "windows-targets"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9b724f72796e036ab90c1021d4780d4d3d648aca59e491e6b98e725b84e99973"
+dependencies = [
+ "windows_aarch64_gnullvm",
+ "windows_aarch64_msvc",
+ "windows_i686_gnu",
+ "windows_i686_gnullvm",
+ "windows_i686_msvc",
+ "windows_x86_64_gnu",
+ "windows_x86_64_gnullvm",
+ "windows_x86_64_msvc",
+]
+
+[[package]]
+name = "windows_aarch64_gnullvm"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "32a4622180e7a0ec044bb555404c800bc9fd9ec262ec147edd5989ccd0c02cd3"
+
+[[package]]
+name = "windows_aarch64_msvc"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09ec2a7bb152e2252b53fa7803150007879548bc709c039df7627cabbd05d469"
+
+[[package]]
+name = "windows_i686_gnu"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e9b5ad5ab802e97eb8e295ac6720e509ee4c243f69d781394014ebfe8bbfa0b"
+
+[[package]]
+name = "windows_i686_gnullvm"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0eee52d38c090b3caa76c563b86c3a4bd71ef1a819287c19d586d7334ae8ed66"
+
+[[package]]
+name = "windows_i686_msvc"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "240948bc05c5e7c6dabba28bf89d89ffce3e303022809e73deaefe4f6ec56c66"
+
+[[package]]
+name = "windows_x86_64_gnu"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "147a5c80aabfbf0c7d901cb5895d1de30ef2907eb21fbbab29ca94c5b08b1a78"
+
+[[package]]
+name = "windows_x86_64_gnullvm"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "24d5b23dc417412679681396f2b49f3de8c1473deb516bd34410872eff51ed0d"
+
+[[package]]
+name = "windows_x86_64_msvc"
+version = "0.52.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "589f6da84c646204747d1270a2a5661ea66ed1cced2631d546fdfb155959f9ec"
+
 [[package]]
 name = "wit-bindgen"
 version = "0.51.0"

Cargo.toml

@@ -7,6 +7,9 @@ edition = "2024"
 crossterm = "0.29"
 ratatui = { version = "0.30", features = ["crossterm"] }
 
+[dev-dependencies]
+insta = "1.33"
+
 [lints.clippy]
 pedantic = "warn"
 unused_trait_names = "warn"

src/main.rs

@@ -1,4 +1,6 @@
 mod terminal_guard;
+/// UI components (todo list)
+mod todo_list;
 
 use core::time::Duration;
 use crossterm::event::{self, EnableMouseCapture, Event, KeyCode};
@@ -6,11 +8,11 @@ use crossterm::execute;
 use crossterm::terminal::{EnterAlternateScreen, enable_raw_mode};
 use ratatui::Terminal;
 use ratatui::backend::CrosstermBackend;
-use ratatui::style::Style;
-use ratatui::widgets::{Block, Borders, List, ListItem, ListState};
 use std::io::{self, Read as _};
 use terminal_guard::TerminalModeGuard;
+use todo_list::TodoList;
 
+#[allow(clippy::wildcard_enum_match_arm)]
 fn main() -> Result<(), Box<dyn std::error::Error>> {
     let mut input = String::new();
     io::stdin().read_to_string(&mut input)?;
@@ -24,7 +26,7 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
         .lines()
         .map(std::string::ToString::to_string)
         .collect();
-    let mut marked = vec![false; lines.len()];
+    let mut todo = TodoList::with_lines(lines);
 
     enable_raw_mode()?;
     let mut stdout = std::io::stdout();
@@ -35,33 +37,9 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
     let backend = CrosstermBackend::new(stdout);
     let mut terminal = Terminal::new(backend)?;
 
-    let mut state = ListState::default();
-    if !lines.is_empty() {
-        state.select(Some(0));
-    }
-
     loop {
         terminal.draw(|f| {
-            let size = f.area();
+            todo.draw(f);
-
-            let items: Vec<ListItem> = lines
-                .iter()
-                .zip(marked.iter())
-                .map(|(text, marked)| {
-                    let prefix = if *marked { 'x' } else { ' ' };
-                    ListItem::new(format!("[{prefix}] {text}"))
-                })
-                .collect();
-
-            let list = List::new(items)
-                .block(
-                    Block::default()
-                        .borders(Borders::ALL)
-                        .title("Lines (space to mark, q to quit)"),
-                )
-                .highlight_style(Style::default().bold().yellow().on_dark_gray());
-
-            f.render_stateful_widget(list, size, &mut state);
         })?;
 
         if event::poll(Duration::from_millis(100))? {
@@ -69,23 +47,23 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
                 Event::Key(key) => match key.code {
                     KeyCode::Char('q') => break,
                     KeyCode::Up => {
-                        if let Some(i) = state.selected() {
+                        if let Some(i) = todo.state.selected() {
-                            state.select(Some(i.saturating_sub(1)));
+                            todo.state.select(Some(i.saturating_sub(1)));
                         }
                     }
                     KeyCode::Down => {
-                        if let Some(i) = state.selected() {
+                        if let Some(i) = todo.state.selected() {
-                            state.select(Some((i + 1).min(lines.len() - 1)));
+                            todo.state.select(Some((i + 1).min(todo.lines.len() - 1)));
                         }
                     }
                     KeyCode::Char(' ') => {
-                        if let Some(i) = state.selected() {
+                        if let Some(i) = todo.state.selected() {
-                            let Some(marked_cell) = marked.get_mut(i) else {
+                            let Some(marked_cell) = todo.marked.get_mut(i) else {
                                 return Err("Index out of bounds".into());
                             };
                             if !*marked_cell {
-                                let next = lines.len().min(i + 1);
+                                let next = todo.lines.len().min(i + 1);
-                                state.select(Some(next));
+                                todo.state.select(Some(next));
                             }
                             *marked_cell = !*marked_cell;
                         }
@@ -98,10 +76,14 @@ fn main() -> Result<(), Box<dyn std::error::Error>> {
                 Event::Mouse(s) => {
                     if s.kind == event::MouseEventKind::Down(event::MouseButton::Left) {
                         let area = terminal.size()?;
-                        if s.row > area.height && s.row < area.height + area.height {
+                        if let Some(row_idx) = s
-                            let idx = (s.row - area.height - 1) as usize;
+                            .row
-                            if idx < lines.len() {
+                            .checked_sub(area.height + 1)
-                                state.select(Some(idx));
+                            .filter(|_| s.row < area.height.saturating_add(area.height))
+                        {
+                            let idx = usize::from(row_idx);
+                            if idx < todo.lines.len() {
+                                todo.state.select(Some(idx));
                             }
                         }
                     }

src/terminal_guard.rs

@@ -11,7 +11,10 @@ pub struct TerminalModeGuard;
 impl TerminalModeGuard {}
 
 impl Drop for TerminalModeGuard {
-    #[allow(clippy::let_underscore_must_use, reason = "We want to ignore errors during cleanup.")]
+    #[allow(
+        clippy::let_underscore_must_use,
+        reason = "We want to ignore errors during cleanup."
+    )]
     fn drop(&mut self) {
         let _ = disable_raw_mode();
         let mut stdout = std::io::stdout();

src/todo_list.rs

@@ -0,0 +1,56 @@
+use ratatui::style::Style;
+use ratatui::widgets::{Block, Borders, List, ListItem, ListState};
+// use Frame via the crate root type `ratatui::Frame` in the signature below
+
+/// A simple todo/list view that owns the lines, marked flags and selection state.
+pub struct TodoList {
+    pub lines: Vec<String>,
+    pub marked: Vec<bool>,
+    pub state: ListState,
+    pub title: String,
+}
+
+impl TodoList {
+    /// Create a new `TodoList` from lines.
+    pub fn new(lines: Vec<String>) -> Self {
+        let mut state = ListState::default();
+        if !lines.is_empty() {
+            state.select(Some(0));
+        }
+
+        Self {
+            lines,
+            marked: vec![false; state.selected().map(|_| 0).unwrap_or(0)],
+            state,
+            title: "Lines (space to mark, q to quit)".to_string(),
+        }
+    }
+
+    /// Convenience constructor that ensures marked has same length as lines.
+    pub fn with_lines(lines: Vec<String>) -> Self {
+        let mut s = Self::new(lines);
+        s.marked = vec![false; s.lines.len()];
+        s
+    }
+
+    /// Draw the list into a `ratatui` frame.
+    pub fn draw(&mut self, f: &mut ratatui::Frame<'_>) {
+        let size = f.area();
+
+        let items: Vec<ListItem> = self
+            .lines
+            .iter()
+            .zip(self.marked.iter())
+            .map(|(text, marked)| {
+                let prefix = if *marked { 'x' } else { ' ' };
+                ListItem::new(format!("[{prefix}] {text}"))
+            })
+            .collect();
+
+        let list = List::new(items)
+            .block(Block::default().borders(Borders::ALL).title(&*self.title))
+            .highlight_style(Style::default().bold().yellow().on_dark_gray());
+
+        f.render_stateful_widget(list, size, &mut self.state);
+    }
+}

tests/snapshots/ui_snapshot__ui_snapshot_basic.snap

@@ -0,0 +1,23 @@
+---
+source: tests/ui_snapshot.rs
+assertion_line: 50
+expression: out
+---
+Buffer {
+    area: Rect { x: 0, y: 0, width: 40, height: 10 },
+    content: [
+        "┌Lines (space to mark, q to quit)──────┐",
+        "│[ ] first                             │",
+        "│[x] second                            │",
+        "│[ ] third                             │",
+        "│                                      │",
+        "│                                      │",
+        "│                                      │",
+        "│                                      │",
+        "│                                      │",
+        "└──────────────────────────────────────┘",
+    ],
+    styles: [
+        x: 0, y: 0, fg: Reset, bg: Reset, underline: Reset, modifier: NONE,
+    ]
+}

tests/ui_snapshot.rs

@@ -0,0 +1,61 @@
+use ratatui::Terminal;
+use ratatui::backend::TestBackend;
+use ratatui::buffer::Buffer;
+use ratatui::layout::Rect;
+use ratatui::style::Style;
+use ratatui::widgets::{Block, Borders, List, ListItem, ListState};
+
+fn render_list_into_buffer(
+    lines: &[&str],
+    marked: &[bool],
+    selected: Option<usize>,
+    width: u16,
+    height: u16,
+) -> Buffer {
+    let backend = TestBackend::new(width.into(), height.into());
+    let mut terminal = Terminal::new(backend).expect("create terminal");
+
+    let lines_vec: Vec<ListItem> = lines
+        .iter()
+        .zip(marked.iter())
+        .map(|(text, marked)| {
+            let prefix = if *marked { 'x' } else { ' ' };
+            ListItem::new(format!("[{prefix}] {text}"))
+        })
+        .collect();
+
+    let mut state = ListState::default();
+    state.select(selected);
+
+    terminal
+        .draw(|f| {
+            let size = Rect::new(0, 0, width, height);
+
+            let list = List::new(lines_vec.clone())
+                .block(
+                    Block::default()
+                        .borders(Borders::ALL)
+                        .title("Lines (space to mark, q to quit)"),
+                )
+                .highlight_style(Style::default());
+
+            f.render_stateful_widget(list, size, &mut state);
+        })
+        .expect("draw");
+
+    // Extract the underlying backend buffer (clone to own it)
+    let backend = terminal.backend();
+    let buf = backend.buffer().clone();
+    buf
+}
+
+#[test]
+fn ui_snapshot_basic() {
+    let lines = ["first", "second", "third"];
+    let marked = [false, true, false];
+    let buf = render_list_into_buffer(&lines, &marked, Some(1), 40, 10);
+
+    // Use the buffer's debug representation for snapshotting
+    let out = format!("{buf:#?}");
+    insta::assert_snapshot!(out);
+}