TreeIndex test sporadic failure

[wvwwvwwv]

---- tests::correctness::treeindex_test::remove stdout ----
thread '' panicked at 'assertion failed: (left == right)
left: 1,
right: 2: 2 1 2', src/tests/correctness.rs:522:21
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace
thread 'tests::correctness::treeindex_test::remove' panicked at 'called Result::unwrap() on an Err value: Any { .. }', src/tests/correctness.rs:528:27

[wvwwvwwv]

another occurrence.

thread '' panicked at 'assertion failed: (left == right)
left: 17,
right: 16: 17 16 16', src/tests/correctness.rs:511:21
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace

[wvwwvwwv]

The latest change causes the issue to resurface: now it's always on remove_if.

thread '' panicked at 'assertion failed: (left == right)
left: 18,
right: 17: 18 18 17', src/tests/correctness.rs:816:21
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace
thread 'tests::correctness::treeindex_test::remove' panicked at 'called Result::unwrap() on an Err value: Any { .. }', src/tests/correctness.rs:822:27

thread '' panicked at 'assertion failed: (left == right)
left: 16,
right: 15: 16 16 15', src/tests/correctness.rs:816:21
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace
thread 'tests::correctness::treeindex_test::remove' panicked at 'called Result::unwrap() on an Err value: Any { .. }', src/tests/correctness.rs:822:27

---- tests::correctness::treeindex_test::remove stdout ----
thread '' panicked at 'assertion failed: (left == right)
left: 11,
right: 10: 11 11 10', src/tests/correctness.rs:816:21
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace
thread 'tests::correctness::treeindex_test::remove' panicked at 'called Result::unwrap() on an Err value: Any { .. }', src/tests/correctness.rs:822:27

c939735

=> If the effect of the change is minuscule, I'll just revert it.

[wvwwvwwv]

reverted