Added tests to Assets chain-extension

[PierreOssun]

Pull Request Summary
Added tests to Asset chain-extension

Check list

• added unit tests

[github-actions]

Package	Line Rate	Branch Rate	Health
frame/dapps-staking/src/pallet	87%	0%	✔
frame/custom-signatures/src	52%	0%	➖
chain-extensions/types/xvm/src	0%	0%	❌
chain-extensions/xvm/src	0%	0%	❌
frame/contracts-migration/src	0%	0%	❌
precompiles/sr25519/src	79%	0%	➖
precompiles/utils/macro/tests	0%	0%	❌
precompiles/utils/src	69%	0%	➖
chain-extensions/types/assets/src	0%	0%	❌
frame/dapps-staking/src	82%	0%	✔
frame/block-reward/src	80%	0%	✔
precompiles/assets-erc20/src	76%	0%	➖
frame/xc-asset-config/src	50%	0%	➖
frame/pallet-xvm/src/pallet	8%	0%	❌
precompiles/substrate-ecdsa/src	78%	0%	➖
precompiles/utils/macro/src	0%	0%	❌
precompiles/xcm/src	85%	0%	✔
chain-extensions/pallet-assets/src	60%	0%	➖
frame/collator-selection/src	76%	0%	➖
frame/pallet-xcm/src	53%	0%	➖
primitives/xcm/src	62%	0%	➖
chain-extensions/dapps-staking/src	0%	0%	❌
frame/pallet-xvm/src	5%	0%	❌
precompiles/xvm/src	61%	0%	➖
precompiles/dapps-staking/src	93%	0%	✔
chain-extensions/types/dapps-staking/src	0%	0%	❌
Summary	60% (2832 / 4756)	0% (0 / 0)	➖

Minimum allowed line rate is 50%

[PierreOssun]

@Dinonard I think we can close this