### Question:
PrimitiveLongCollections { public static int indexOf( PrimitiveLongIterator iterator, long item ) { for ( int i = 0; iterator.hasNext(); i++ ) { if ( item == iterator.next() ) { return i; } } return -1; } private  PrimitiveLongCollections(); static PrimitiveLongIterator iterator( final long... items ); static PrimitiveLongIterator concat( PrimitiveLongIterator... primitiveLongIterators ); static PrimitiveLongIterator concat( Iterable<PrimitiveLongIterator> primitiveLongIterators ); static PrimitiveLongIterator filter( PrimitiveLongIterator source, final LongPredicate filter ); static PrimitiveLongResourceIterator filter( PrimitiveLongResourceIterator source, final LongPredicate filter ); static PrimitiveLongIterator range( long start, long end ); static long single( PrimitiveLongIterator iterator, long defaultItem ); static int indexOf( PrimitiveLongIterator iterator, long item ); static PrimitiveLongSet asSet( Collection<Long> collection ); static PrimitiveLongSet asSet( PrimitiveLongIterator iterator ); static PrimitiveLongSet asSet( PrimitiveLongSet set ); static PrimitiveLongSet asSet( long... values ); static PrimitiveLongObjectMap<T> copy( PrimitiveLongObjectMap<T> original ); static int count( PrimitiveLongIterator iterator ); static long[] asArray( PrimitiveLongIterator iterator ); static long[] asArray( Iterator<Long> iterator ); static PrimitiveLongIterator emptyIterator(); static PrimitiveLongIterator toPrimitiveIterator( final Iterator<Long> iterator ); static PrimitiveLongSet emptySet(); static PrimitiveLongSet setOf( long... values ); static Iterator<T> map( final LongFunction<T> mapFunction, final PrimitiveLongIterator source ); static List<Long> asList( PrimitiveLongIterator iterator ); static Iterator<Long> toIterator( final PrimitiveLongIterator primIterator ); static PrimitiveLongResourceIterator resourceIterator( final PrimitiveLongIterator iterator,
            final Resource resource ); static Set<Long> toSet( PrimitiveLongSet set ); static Set<Long> toSet( PrimitiveLongIterator iterator ); static long[] deduplicate( long[] values ); static final long[] EMPTY_LONG_ARRAY; }### Answer:
@Test void indexOf() { PrimitiveLongIterable items = () -> PrimitiveLongCollections.iterator( 10, 20, 30 ); assertEquals( -1, PrimitiveLongCollections.indexOf( items.iterator(), 55 ) ); assertEquals( 0, PrimitiveLongCollections.indexOf( items.iterator(), 10 ) ); assertEquals( 1, PrimitiveLongCollections.indexOf( items.iterator(), 20 ) ); assertEquals( 2, PrimitiveLongCollections.indexOf( items.iterator(), 30 ) ); }