Assert a std::io::Read read_to_string() contains a pattern.
Pseudocode: (reader.read_to_string(a) ⇒ a) contains (expr into string)
use std::io::Read; let mut reader = "hello".as_bytes(); let containee = "ell"; assert_io_read_to_string_contains!(reader, &containee);
assert_io_read_to_string_contains
assert_io_read_to_string_contains_as_result
debug_assert_io_read_to_string_contains