add random blobs

consensus/types/src/eth_spec.rs

@@ -255,6 +255,11 @@ pub trait EthSpec:
     fn max_blobs_per_block() -> usize {
         Self::MaxBlobsPerBlock::to_usize()
     }
+
+    /// Returns the `BYTES_PER_BLOB` constant for this specification.
+    fn bytes_per_blob() -> usize {
+        Self::BytesPerBlob::to_usize()
+    }
 }
 
 /// Macro to inherit some type values from another EthSpec.

consensus/types/src/test_utils/test_random/bitfield.rs

@@ -4,8 +4,24 @@ use smallvec::smallvec;
 
 impl<N: Unsigned + Clone> TestRandom for BitList<N> {
     fn random_for_test(rng: &mut impl RngCore) -> Self {
-        let mut raw_bytes = smallvec![0; std::cmp::max(1, (N::to_usize() + 7) / 8)];
+        let initial_len = std::cmp::max(1, (N::to_usize() + 7) / 8);
+        let mut raw_bytes = smallvec![0; initial_len];
         rng.fill_bytes(&mut raw_bytes);
+
+        let highest_set_bit = raw_bytes
+            .iter()
+            .enumerate()
+            .rev()
+            .find(|(_, byte)| **byte > 0)
+            .map(|(i, byte)| i * 8 + 7 - byte.leading_zeros() as usize)
+            .unwrap_or(0);
+
+        let actual_len = highest_set_bit / 8 + 1;
+
+        if actual_len < initial_len {
+            raw_bytes.truncate(actual_len);
+        }
+
         Self::from_bytes(raw_bytes).expect("we generate a valid BitList")
     }
 }