UniqueItems Constraint

UniqueItemsConstraint tests that an IEnumerable contains no duplicate items.

Usage

Is.Unique

Modifiers

.IgnoreCase
.IgnoreWhiteSpace              // NUnit 4.2+
.Using(IComparer comparer)
.Using(IEqualityComparer comparer)
.Using<T>(IComparer<T> comparer)
.Using<T>(IEqualityComparer<T> comparer)
.Using<T>(Comparison<T> comparer)
.Using<T>(Func<T, T, bool> comparer)
.UsingPropertiesComparer()     // NUnit 4.1+

Examples

[Test]
public void UniqueItemsConstraint_Examples()
{
    int[] numbers = { 1, 2, 3, 4, 5 };
    string[] names = { "Alice", "Bob", "Carol" };

    // Basic uniqueness check
    Assert.That(numbers, Is.Unique);
    Assert.That(names, Is.Unique);

    // Fails: contains duplicates
    Assert.That(new[] { 1, 2, 2, 3 }, Is.Not.Unique);

    // Case-insensitive uniqueness
    Assert.That(new[] { "Alice", "ALICE" }, Is.Unique);               // Passes: different case
    Assert.That(new[] { "Alice", "ALICE" }, Is.Not.Unique.IgnoreCase); // Passes: same when ignoring case
}

Notes

  1. An empty collection is considered unique (no duplicates possible).
  2. Duplicates are determined using the default equality comparer unless a custom comparer is specified.

See Also