public static void CollectionExtensionTests()
{
var nullEnumerable = (IEnumerable <string>)null;
var empty = new string[0];
var notSparse = new string[] { "a", "b", "c" };
var sparse = new string[] { "a", null };
var numbers = new int[] { 1, 2, 3 };
var emptyNumbers = new int[0];
// NullOrEmpty
Assert.True(nullEnumerable.NullOrEmpty());
Assert.True(new ListWrapper <string>(empty).NullOrEmpty());
Assert.True(new ReadOnlyListWrapper <string>(empty).NullOrEmpty());
Assert.True(new EnumerableWrapper <string>(empty).NullOrEmpty());
Assert.False(new ListWrapper <int>(numbers).NullOrEmpty());
Assert.False(new ReadOnlyListWrapper <int>(numbers).NullOrEmpty());
Assert.False(new EnumerableWrapper <int>(numbers).NullOrEmpty());
// NullOrSparse
Assert.True(nullEnumerable.NullOrSparse());
Assert.False(new ListWrapper <string>(empty).NullOrSparse());
Assert.False(new ReadOnlyListWrapper <string>(empty).NullOrSparse());
Assert.False(new EnumerableWrapper <string>(empty).NullOrSparse());
Assert.True(new ListWrapper <string>(sparse).NullOrSparse());
Assert.True(new ReadOnlyListWrapper <string>(sparse).NullOrSparse());
Assert.True(new EnumerableWrapper <string>(sparse).NullOrSparse());
Assert.False(new ListWrapper <string>(notSparse).NullOrSparse());
Assert.False(new ReadOnlyListWrapper <string>(notSparse).NullOrSparse());
Assert.False(new EnumerableWrapper <string>(notSparse).NullOrSparse());
// NullEmptyOrSparse
Assert.True(nullEnumerable.NullEmptyOrSparse());
Assert.True(new ListWrapper <string>(empty).NullEmptyOrSparse());
Assert.True(new ReadOnlyListWrapper <string>(empty).NullEmptyOrSparse());
Assert.True(new EnumerableWrapper <string>(empty).NullEmptyOrSparse());
Assert.True(new ListWrapper <string>(sparse).NullEmptyOrSparse());
Assert.True(new ReadOnlyListWrapper <string>(sparse).NullEmptyOrSparse());
Assert.True(new EnumerableWrapper <string>(sparse).NullEmptyOrSparse());
Assert.False(new ListWrapper <string>(notSparse).NullEmptyOrSparse());
Assert.False(new ReadOnlyListWrapper <string>(notSparse).NullEmptyOrSparse());
Assert.False(new EnumerableWrapper <string>(notSparse).NullEmptyOrSparse());
// Contains(predicate)
// NOTE: mostly tested implicitly by NullOrSparse/NullEmptyOrSparse
Assert.Throws <ArgumentNullException>(() => CoreExtensions.Contains(sequence: (IEnumerable <int>)null, predicate: i => true));
Assert.Throws <ArgumentNullException>(() => CoreExtensions.Contains(sequence: numbers, predicate: null));
// FirstOrNullable()
Assert.Throws <ArgumentNullException>(() => CoreExtensions.FirstOrNullable(sequence: (IEnumerable <int>)null));
Assert.False(new ListWrapper <int>(emptyNumbers).FirstOrNullable().HasValue);
Assert.False(new ReadOnlyListWrapper <int>(emptyNumbers).FirstOrNullable().HasValue);
Assert.False(new EnumerableWrapper <int>(emptyNumbers).FirstOrNullable().HasValue);
Assert.AreEqual(1, new ListWrapper <int>(numbers).FirstOrNullable().Value);
Assert.AreEqual(1, new ReadOnlyListWrapper <int>(numbers).FirstOrNullable().Value);
Assert.AreEqual(1, new EnumerableWrapper <int>(numbers).FirstOrNullable().Value);
// FirstOrNullable(predicate)
Assert.AreEqual(3, numbers.FirstOrNullable(i => i == 3).Value);
Assert.False(numbers.FirstOrNullable(i => i == 4).HasValue);
}