add, fix tests

crates/wasi-c2/src/random.rs

@@ -5,6 +5,8 @@ pub trait WasiRandom {
     fn get(&self, buf: &mut [u8]) -> Result<(), Error>;
 }
 
+/// Implement `WasiRandom` using the `getrandom` crate, which selects your system's best entropy
+/// source.
 pub struct GetRandom;
 
 impl WasiRandom for GetRandom {
@@ -14,6 +16,7 @@ impl WasiRandom for GetRandom {
     }
 }
 
+/// Implement `WasiRandom` using a deterministic cycle of bytes.
 pub struct Deterministic {
     sequence: RefCell<std::iter::Cycle<std::vec::IntoIter<u8>>>,
 }
@@ -35,3 +38,17 @@ impl WasiRandom for Deterministic {
         Ok(())
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    #[test]
+    fn deterministic() {
+        let det = Deterministic::new(vec![1, 2, 3, 4]);
+        let mut buf = vec![0; 1024];
+        det.get(&mut buf).expect("get randomness");
+        for (ix, b) in buf.iter().enumerate() {
+            assert_eq!(*b, (ix % 4) as u8 + 1)
+        }
+    }
+}