Test multiple blocks/txs per block.

Better debug tracing.

substrate/wasm-runtime/polkadot/src/lib.rs

@@ -37,6 +37,7 @@ pub mod runtime;
 
 use runtime_std::prelude::*;
 use codec::Slicable;
+use runtime_std::print;
 use primitives::{Block, UncheckedTransaction};
 
 /// Execute a block, with `input` being the canonical serialisation of the block. Returns the
@@ -53,4 +54,14 @@ pub fn execute_transaction(input: &[u8]) -> Vec<u8> {
 	Vec::new()
 }
 
-impl_stubs!(execute_block, execute_transaction);
+/// Run whatever tests we have.
+pub fn run_tests(input: &[u8]) -> Vec<u8> {
+	print("run_tests...");
+	let block = Block::from_slice(input).unwrap();
+	print("deserialised block.");
+	let stxs = block.transactions.iter().map(Slicable::to_vec).collect::<Vec<_>>();
+	print("reserialised transactions.");
+	[stxs.len() as u8].to_vec()
+}
+
+impl_stubs!(execute_block, execute_transaction, run_tests);