Macro context 

macro_rules! context {
    ($($key:expr => $value:expr,)+) => { ... };
    ($($key:expr => $value:expr),*) => { ... };
}

this macro simplifies creation of ad-hoc tera::Contexts.

let mut context = tera::Context::new();
context.insert("template-engine", "tera");
assert_eq!(context, context! { "template-engine" => "tera" });