We have a test that is intended to cover the case where the user specifies all 3 compressors. However, we don't ever actually run our tests with all 3 of the compressor feature flags enabled, which is necessary for this test.
(We were doing that by accident until recently but that has been corrected as of https://github.com/mongodb/mongo-rust-driver/pull/819).

It would be good to either update evergreen to somehow actually run this test, or if we decide the coverage is not that useful we could remove it.