Add a small test checking that pollables can be used many times

Author: elliottt

crates/test-programs/src/bin/preview2_stream_pollable_correct.rs

@@ -1,11 +1,27 @@
-use test_programs::wasi::cli::stdin;
-use test_programs::wasi::io::streams;
+use test_programs::wasi::cli::{stdin, stdout};
 
 fn main() {
-    let stdin: streams::InputStream = stdin::get_stdin();
+    let stdin = stdin::get_stdin();
     let stdin_pollable = stdin.subscribe();
     stdin_pollable.block();
     assert!(stdin_pollable.ready(), "after blocking, pollable is ready");
     drop(stdin_pollable);
     drop(stdin);
+
+    // Pollables can be used many times over their lifetime
+    let stdout = stdout::get_stdout();
+    let stdout_pollable = stdout.subscribe();
+
+    let chunk = [b'a'; 50];
+    for _ in 1..10 {
+        stdout_pollable.block();
+        assert!(stdout_pollable.ready(), "after blocking, pollable is ready");
+
+        let n = stdout.check_write().unwrap() as usize;
+        assert!(n >= chunk.len());
+        stdout.write(&chunk).unwrap();
+    }
+
+    drop(stdout_pollable);
+    drop(stdout);
 }