Design and implement a way to help user setup the test environment

[yanganto]

It is good and clear for a user building ewasm contract in a single file.

#[derive(Default, Serialize, Deserialize)]
struct SimpleStruct {
    trust: bool,
    description: String,
}

#[ewasm_fn]
fn check_input_object(s: SimpleStruct) -> Result<()> {
    if !s.trust {
        return Err(Error::NotTrustedInput.into());
    }
    Ok(())
}

#[ewasm_main]
fn main() -> Result<()> {
    let contract = Contract::new()?;
    match contract.get_function_selector()? {
        fn_sig!(check_input_object) => input_from!(contract, check_input_object)?,
        _ => return Err(Error::UnknownHandle.into()),
    };

    Ok(())
}

#[ewasm_test]
mod tests {
    #[ewasm_test]
    fn test_execute_basic_operation() {
        let mut simple_struct = SimpleStruct::default();
        ewasm_assert_eq!(
            check_input_object(simple_struct),
            vec![110, 111, 116, 32, 116, 114, 117, 115, 116, 32, 105, 110, 112, 117, 116]
        )
    }
}

Additional issues need to be solved and figure out before implementing

• The mod test is built with target x86_64-unknown-linux-gnu, and the other part is built with target wasm32-unknown-unknown, because wasmedge and the runtime environment only works x86_64-unknown-linux-gnu but not wasm32-unknown-unknown

Relating references

• https://github.com/rust-lang/rfcs/blob/master/text/2318-custom-test-frameworks.md
• Tracking issue for eRFC 2318, Custom test frameworks rust-lang/rust#50297
• eRFC: Custom test frameworks rust-lang/rfcs#2318