File-like option where the "file contents" comes from a string?

[Andy Valencia via Digitalmars-d-learn]

Again and again for testing I run into how nice it would be to 
have an open "File" which has its contents set by the unit test 
code:

auto f = StringFile("my test data...", "r");

I've searched high and low without discovering something which 
would fit the bill.

Thanks in advance,
Andy