feat: Add initial unit tests for the application

This commit introduces the first set of unit tests for the application.
It includes tests for character entry and rendering of the initial empty application state.

Co-authored-by: Gemini <[email protected]>

Author: nikomatsakis

Cargo.lock

@@ -9,3 +9,6 @@ crossterm = { version = "0.28", features = ["event-stream"] }
 color-eyre = "0.6"
 tokio = { version = "1", features = ["full"] }
 tokio-stream = "0.1"
+
+[dev-dependencies]
+expect-test = "1.4"

Cargo.toml

@@ -0,0 +1,38 @@
+use super::*;
+use expect_test::{Expect, expect};
+use ratatui::{Terminal, backend::TestBackend};
+
+#[test]
+fn test_enter_char() {
+    let mut app = App::new();
+    app.enter_char('a');
+    assert_eq!(app.editor_buffer, "a");
+    assert_eq!(app.editor_cursor, 1);
+}
+
+fn check(app: &App, expected: Expect) {
+    let backend = TestBackend::new(50, 10);
+    let mut terminal = Terminal::new(backend).unwrap();
+    terminal.draw(|frame| app.render(frame)).unwrap();
+    expected.assert_eq(&terminal.backend().to_string());
+}
+
+#[test]
+fn test_render_empty_app() {
+    let app = App::new();
+    check(
+        &app,
+        expect![[r#"
+            "┌Messages────────────────────────────────────────┐"
+            "│                                                │"
+            "│                                                │"
+            "│                                                │"
+            "│                                                │"
+            "│                                                │"
+            "└────────────────────────────────────────────────┘"
+            "┌Editor──────────────────────────────────────────┐"
+            "│                                                │"
+            "└────────────────────────────────────────────────┘"
+        "#]],
+    );
+}

src/app_tests.rs

@@ -296,3 +296,6 @@ impl App {
         }
     }
 }
+
+#[cfg(test)]
+mod app_tests;