message: test: replace is_err in core test
diff: @@ -810,7 +810,7 @@ mod tests {
  let out_point = OutPoint::new_block_hash(header_hash.clone());
  let transaction = TransactionBuilder::default()
  - .input(CellInput::new(out_point, 0))
  + .input(CellInput::new(out_point.clone(), 0))
  .build();
  let mut seen_inputs = FnvHashSet::default();
  @@ -821,7 +821,10 @@ mod tests {
  &header_provider,
  );
  - assert!(result.is_err());
  + assert_eq!(
  + result.err(),
  + Some(UnresolvableError::UnspecifiedInputCell(out_point))
  + );
  }
  #[test]
  @@ -872,7 +875,7 @@ mod tests {
  );
  header_provider.insert_header(header.clone());
  - let transaction = TransactionBuilder::default().dep(out_point).build();
  + let transaction = TransactionBuilder::default().dep(out_point.clone()).build();
  let mut seen_inputs = FnvHashSet::default();
  let result = resolve_transaction(
  @@ -882,7 +885,10 @@ mod tests {
  &header_provider,
  );
  - assert!(result.is_err());
  + assert_eq!(
  + result.err(),
  + Some(UnresolvableError::InvalidHeader(out_point))
  + );
  }
  #[test]
  @@ -915,7 +921,7 @@ mod tests {
  &header_provider,
  );
  - assert!(result.is_err());
  + assert_eq!(result.err(), Some(UnresolvableError::Empty));
  }
  fn generate_block(txs: Vec<Transaction>) -> Block {
  