1 files changed, 65 insertions, 0 deletions
diff --git a/third_party/rust/futures/tests/io_write.rs b/third_party/rust/futures/tests/io_write.rs
new file mode 100644
index 0000000000..6af27553cb
--- /dev/null
+++ b/third_party/rust/futures/tests/io_write.rs
@@ -0,0 +1,65 @@
+use futures::io::AsyncWrite;
+use futures_test::task::panic_context;
+use std::io;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+struct MockWriter {
+    fun: Box<dyn FnMut(&[u8]) -> Poll<io::Result<usize>>>,
+}
+
+impl MockWriter {
+    fn new(fun: impl FnMut(&[u8]) -> Poll<io::Result<usize>> + 'static) -> Self {
+        Self { fun: Box::new(fun) }
+    }
+}
+
+impl AsyncWrite for MockWriter {
+    fn poll_write(
+        self: Pin<&mut Self>,
+        _cx: &mut Context<'_>,
+        buf: &[u8],
+    ) -> Poll<io::Result<usize>> {
+        (self.get_mut().fun)(buf)
+    }
+
+    fn poll_flush(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        panic!()
+    }
+
+    fn poll_close(self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<io::Result<()>> {
+        panic!()
+    }
+}
+
+/// Verifies that the default implementation of `poll_write_vectored`
+/// calls `poll_write` with an empty slice if no buffers are provided.
+#[test]
+fn write_vectored_no_buffers() {
+    let mut writer = MockWriter::new(|buf| {
+        assert_eq!(buf, b"");
+        Err(io::ErrorKind::BrokenPipe.into()).into()
+    });
+    let cx = &mut panic_context();
+    let bufs = &mut [];
+
+    let res = Pin::new(&mut writer).poll_write_vectored(cx, bufs);
+    let res = res.map_err(|e| e.kind());
+    assert_eq!(res, Poll::Ready(Err(io::ErrorKind::BrokenPipe)))
+}
+
+/// Verifies that the default implementation of `poll_write_vectored`
+/// calls `poll_write` with the first non-empty buffer.
+#[test]
+fn write_vectored_first_non_empty() {
+    let mut writer = MockWriter::new(|buf| {
+        assert_eq!(buf, b"four");
+        Poll::Ready(Ok(4))
+    });
+    let cx = &mut panic_context();
+    let bufs = &mut [io::IoSlice::new(&[]), io::IoSlice::new(&[]), io::IoSlice::new(b"four")];
+
+    let res = Pin::new(&mut writer).poll_write_vectored(cx, bufs);
+    let res = res.map_err(|e| e.kind());
+    assert_eq!(res, Poll::Ready(Ok(4)));
+}