Function prepend_unique_prefix 

pub fn prepend_unique_prefix(
    objects: impl IntoIterator<Item = TestObject>,
) -> (String, impl IntoIterator<Item = TestObject>)

Generate a unique prefix ending in a / character, and prepend it to the key in a collection of TestObjects.

Returns the unique prefix an an iterator that yields the modified test objects.

This is useful when running tests against a real S3 bucket, where multiple runs of the same test may write to the bucket so each test’s object keys must be unique