Function assert_contains 

pub fn assert_contains<H, N>(needle: N, haystack: H)
where
    H: Container + Debug,
    N: Borrow<H::Item>,
    H::Item: Debug,

Assert that a haystack contains the given needle.

Uses the Container abstraction so it works with slices, vectors, sets, maps (by key), strings, and ranges. The error message includes both the container and the item for quick debugging.

Panics

Panics if haystack.contains(needle) returns false.