chore: checkpoint before Python removal

vendor/futures/tests/io_read_exact.rs

@@ -0,0 +1,17 @@
+use futures::executor::block_on;
+use futures::io::AsyncReadExt;
+
+#[test]
+fn read_exact() {
+    let mut reader: &[u8] = &[1, 2, 3, 4, 5];
+    let mut out = [0u8; 3];
+
+    let res = block_on(reader.read_exact(&mut out)); // read 3 bytes out
+    assert!(res.is_ok());
+    assert_eq!(out, [1, 2, 3]);
+    assert_eq!(reader.len(), 2);
+
+    let res = block_on(reader.read_exact(&mut out)); // read another 3 bytes, but only 2 bytes left
+    assert!(res.is_err());
+    assert_eq!(reader.len(), 0);
+}