Tests for unsound Windows file methods

Author: ChrisDenton

std/src/sys/windows/handle.rs

@@ -1,5 +1,8 @@
 #![unstable(issue = "none", feature = "windows_handle")]
 
+#[cfg(test)]
+mod tests;
+
 use crate::cmp;
 use crate::io::{self, ErrorKind, IoSlice, IoSliceMut, Read, ReadBuf};
 use crate::mem;

std/src/sys/windows/handle/tests.rs

@@ -0,0 +1,22 @@
+use crate::sys::pipe::{anon_pipe, Pipes};
+use crate::{thread, time};
+
+/// Test the synchronous fallback for overlapped I/O.
+#[test]
+fn overlapped_handle_fallback() {
+    // Create some pipes. `ours` will be asynchronous.
+    let Pipes { ours, theirs } = anon_pipe(true, false).unwrap();
+
+    let async_readable = ours.into_handle();
+    let sync_writeable = theirs.into_handle();
+
+    thread::scope(|_| {
+        thread::sleep(time::Duration::from_millis(100));
+        sync_writeable.write(b"hello world!").unwrap();
+    });
+
+    // The pipe buffer starts empty so reading won't complete synchronously unless
+    // our fallback path works.
+    let mut buffer = [0u8; 1024];
+    async_readable.read(&mut buffer).unwrap();
+}