nbio(tests): fill the socket until sending blocks

tests/core/nbio/net.odin

@@ -302,13 +302,25 @@ poll :: proc(t: ^testing.T) {
 			on_poll1 :: proc(op: ^nbio.Operation, t: ^testing.T, can_recv: ^bool) {
 				ev(t, op.poll.result, nil)
 
-				// Send 4 GB of data, which in my experience causes a Would_Block error because we filled up the internal buffer.
+				// Fill the socket until sending actually blocks. How much that takes depends
+				// on the machine's socket buffers, so keep sending rather than assuming a
+				// fixed amount does it. Nothing is reading yet, so this terminates.
 				buf, mem_err := make([]byte, mem.Gigabyte*4, context.temp_allocator)
 				ev(t, mem_err, nil)
 
 				// Use `core:net` as example external code that doesn't care about the event loop.
 				net.set_blocking(op.poll.socket, false)
-				n, send_err := net.send(op.poll.socket, buf)
+
+				n: int
+				send_err: net.Network_Error
+				for _ in 0..<16 {
+					sent: int
+					sent, send_err = net.send(op.poll.socket, buf)
+					n += sent
+					if send_err != nil {
+						break
+					}
+				}
 				ev(t, send_err, net.TCP_Send_Error.Would_Block)
 
 				log.debugf("blocking after %M", n)