error[E0596]: cannot borrow `*db_ref1` as mutable, as it is behind a `&` reference
 --> tests/fail/open_with_multiple_refs_as_single_threaded.rs:9:5
  |
9 |     db_ref1.create_cf("cf1", &opts).unwrap();
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `db_ref1` is a `&` reference, so the data it refers to cannot be borrowed as mutable
  |
help: consider changing this to be a mutable reference
  |
6 |     let db_ref1 = &mut db;
  |                   ~~~~~~~

error[E0596]: cannot borrow `*db_ref2` as mutable, as it is behind a `&` reference
  --> tests/fail/open_with_multiple_refs_as_single_threaded.rs:10:5
   |
10 |     db_ref2.create_cf("cf2", &opts).unwrap();
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `db_ref2` is a `&` reference, so the data it refers to cannot be borrowed as mutable
   |
help: consider changing this to be a mutable reference
   |
7  |     let db_ref2 = &mut db;
   |                   ~~~~~~~