Add a random number of transactions to generated blocks, rather than always 2 (#2567)

* Add 1 to 3 transactions to generated blocks, rather than always 2

This change improves test coverage.

As a side-effect, it reduces the average number of generated
transactions, which should improve performance.

* Add 1 to max_size generated transparent inputs, rather than always max_size

Co-authored-by: Deirdre Connolly <deirdre@zfnd.org>

zebra-chain/src/block/arbitrary.rs

@@ -16,6 +16,7 @@ use crate::{
         GENESIS_PREVIOUS_BLOCK_HASH,
     },
     serialization,
+    transaction::arbitrary::MAX_ARBITRARY_ITEMS,
     transparent::{new_transaction_ordered_outputs, CoinbaseSpendRestriction},
     work::{difficulty::CompactDifficulty, equihash},
 };
@@ -321,7 +322,14 @@ impl Arbitrary for Block {
     type Parameters = LedgerState;
 
     fn arbitrary_with(ledger_state: Self::Parameters) -> Self::Strategy {
-        let transactions_strategy = Transaction::vec_strategy(ledger_state, 2);
+        let transactions_strategy =
+            (1..MAX_ARBITRARY_ITEMS).prop_flat_map(move |transaction_count| {
+                Transaction::vec_strategy(ledger_state, transaction_count)
+            });
+
+        // TODO: if needed, fixup:
+        // - history and authorizing data commitments
+        // - the transaction merkle root
 
         (Header::arbitrary_with(ledger_state), transactions_strategy)
             .prop_map(move |(header, transactions)| Self {

zebra-chain/src/transparent/arbitrary.rs

@@ -12,7 +12,7 @@ impl Input {
                 .prop_map(|input| vec![input])
                 .boxed()
         } else {
-            vec(Self::arbitrary_with(None), max_size).boxed()
+            vec(Self::arbitrary_with(None), 1..=max_size).boxed()
         }
     }
 }