A simple contract allows to lend some amount of particular ERC20 token (impl by https://github.com/paritytech/pwasm-token-example) for some interest. It demonstrates how WASM contracts can depend on each other and communicate through ABI. It shows also how to mock callee contract in the test environment.
Install rust with
rustup target add wasm32-unknown-unknown
Install Wasm build util:
cargo install pwasm-utils --bin wasm-build
cargo test --manifest-path="contract/Cargo.toml" --features std