chore: checkpoint before Python removal

vendor/futures/tests/io_window.rs

@@ -0,0 +1,30 @@
+#![allow(clippy::reversed_empty_ranges)] // This is intentional.
+
+use futures::io::Window;
+
+#[test]
+fn set() {
+    let mut buffer = Window::new(&[1, 2, 3]);
+    buffer.set(..3);
+    assert_eq!(buffer.as_ref(), &[1, 2, 3]);
+    buffer.set(3..3);
+    assert_eq!(buffer.as_ref(), &[]);
+    buffer.set(3..=2); // == 3..3
+    assert_eq!(buffer.as_ref(), &[]);
+    buffer.set(0..2);
+    assert_eq!(buffer.as_ref(), &[1, 2]);
+}
+
+#[test]
+#[should_panic]
+fn set_panic_out_of_bounds() {
+    let mut buffer = Window::new(&[1, 2, 3]);
+    buffer.set(2..4);
+}
+
+#[test]
+#[should_panic]
+fn set_panic_start_is_greater_than_end() {
+    let mut buffer = Window::new(&[1, 2, 3]);
+    buffer.set(3..2);
+}