public void PartitionIf_WithEmptyEnumerableAndNullProvider_Throws()
 => Throws <ArgumentNullException>(
     () => ENMRBL_EMPTY.PartitionIf(null).ToList());
 public void PartitionIf_WithEmptyEnumerable_ExpectsSameEnumerable()
 => Utilities.AssertManySequencesEqual(
     ENMRBL_EMPTY.PartitionIf(AlwaysSamePartition),
     ENMRBL_EMPTY);