### Question:
PrimitiveLongCollections { public static int indexOf( LongIterator iterator, long item ) { for ( int i = 0; iterator.hasNext(); i++ ) { if ( item == iterator.next() ) { return i; } } return -1; } private  PrimitiveLongCollections(); static LongIterator iterator( final long... items ); static LongIterator concat( LongIterator... longIterators ); static LongIterator concat( Iterable<LongIterator> primitiveLongIterators ); static LongIterator filter( LongIterator source, final LongPredicate filter ); static LongIterator range( long start, long end ); static int indexOf( LongIterator iterator, long item ); static MutableLongSet asSet( Collection<Long> collection ); static MutableLongSet asSet( LongIterator iterator ); static int count( LongIterator iterator ); static long[] asArray( LongIterator iterator ); static long[] asArray( Iterator<Long> iterator ); static LongIterator toPrimitiveIterator( final Iterator<Long> iterator ); static Iterator<T> map( final LongFunction<T> mapFunction, final LongIterator source ); static List<Long> asList( LongIterator iterator ); static Iterator<Long> toIterator( final LongIterator primIterator ); static PrimitiveLongResourceIterator resourceIterator( final LongIterator iterator,
            final Resource resource ); static Set<Long> toSet( LongSet set ); static Set<Long> toSet( LongIterator iterator ); static long[] deduplicate( long[] values ); static MutableLongSet mergeToSet( LongIterable a, LongIterable b ); static final long[] EMPTY_LONG_ARRAY; }### Answer:
@Test void indexOf() { Supplier<LongIterator> items = () -> PrimitiveLongCollections.iterator( 10, 20, 30 ); assertEquals( -1, PrimitiveLongCollections.indexOf( items.get(), 55 ) ); assertEquals( 0, PrimitiveLongCollections.indexOf( items.get(), 10 ) ); assertEquals( 1, PrimitiveLongCollections.indexOf( items.get(), 20 ) ); assertEquals( 2, PrimitiveLongCollections.indexOf( items.get(), 30 ) ); }