Attribute Macro mockall::automock

#[automock]
Expand description

Automatically generate mock types for structs and traits.

This is by far the easiest way to use Mockall. It works on almost all traits, and almost all structs that have a single impl block. In either case, it will generate a mock struct whose name is the name of the mocked struct/trait prepended with “Mock”. For each method of the original, the mock struct will have a method named expect_whatever that allows you to set expectations. There will also be one checkpoint method that calls checkpoint for every single mocked method.

§Examples

The simplest use case is mocking a no-frills trait

#[automock]
pub trait Foo {
    fn foo(&self, key: i16);
}

let mock = MockFoo::new();

Mocking a structure:

struct Foo {}
#[automock]
impl Foo {
    fn foo(&self) -> u32 {
        // ...
    }
}

You can also mock a trait impl on a struct:

pub trait Foo {
    fn foo(&self, key: i16);
}
struct Bar{}
#[automock]
impl Foo for Bar {
    fn foo(&self, key: i16){
        // ...
    }
}

let mock = MockBar::new();

Mocking a trait with associated types requires adding a metaitem to the attribute:

#[automock(type Item=u32;)]
trait Foo {
    type Item;
    fn foo(&self) -> Self::Item;
}

It can mock a module full of functions. In this case, the mock functions will be found in a module whose name is prepended with mock_.

#[automock]
mod mymod {
    pub fn foo() -> u32 {
       // ...
    }
}

Finally, #[automock] can also mock foreign functions. This works just like mocking a module.

#[automock]
mod ffi {
    extern "C" {
        pub fn foo() -> u32;
    }
}

§Limitations

#[automock] can’t handle everything. There are some cases where you will need to use mock! instead:

  • Mocking a struct that has multiple impl blocks, including structs that implement traits.
  • Mocking a struct or trait defined in another crate.
  • Mocking a trait with trait bounds.
  • If the autogenerated “MockFoo” name isn’t acceptable, and you want to choose your own name for the mock structure.