CollectionOrdered Constraint

CollectionOrderedConstraint tests that an IEnumerable is ordered. An exception is thrown if the actual value does not implement IEnumerable.

Usage

Is.Ordered
Is.Ordered.Ascending
Is.Ordered.Descending
Is.Ordered.By(string propertyName)

Modifiers

.Ascending                     // Ascending order (default)
.Descending                    // Descending order
.By(string propertyName)       // Order by property
.Then                          // Begin next ordering step
.Using(IComparer comparer)
.Using<T>(IComparer<T> comparer)
.Using<T>(Comparison<T> comparer)

Examples

Simple Ordering

[Test]
public void CollectionOrderedConstraint_Examples()
{
    int[] ascending = { 1, 2, 3, 4, 5 };
    int[] descending = { 5, 4, 3, 2, 1 };
    string[] alphabetical = { "Alice", "Bob", "Carol" };

    // Simple ordering
    Assert.That(ascending, Is.Ordered);                  // Default is ascending
    Assert.That(ascending, Is.Ordered.Ascending);        // Explicit ascending
    Assert.That(descending, Is.Ordered.Descending);      // Descending order
    Assert.That(alphabetical, Is.Ordered);               // Alphabetical order

    // Property-based ordering
    string[] byLength = { "a", "bb", "ccc" };
    Assert.That(byLength, Is.Ordered.By("Length"));
    Assert.That(byLength.Reverse(), Is.Ordered.Descending.By("Length"));

    // Custom comparison
    var words = new[] { "apple", "Banana", "cherry" };
    Assert.That(words, Is.Ordered.Using((IComparer<string>)StringComparer.OrdinalIgnoreCase));
}

Multiple Property Ordering

[Test]
public void CollectionOrdered_MultipleProperties_Examples()
{
    var people = new[]
    {
        new { Name = "Alice", Age = 25 },
        new { Name = "Bob", Age = 25 },
        new { Name = "Carol", Age = 30 }
    };

    // Order by Age ascending, then by Name ascending
    Assert.That(people, Is.Ordered.By("Age").Then.By("Name"));
}

Notes

  1. The default ordering is ascending.
  2. The Then modifier separates ordering steps. Each step can have its own Ascending/Descending and Using modifiers.
  3. An empty or single-item collection is always considered ordered.

See Also