CollectionSubset Constraint

CollectionSubsetConstraint tests that one IEnumerable is a subset of another. Every item in the actual collection must be present in the expected collection. An exception is thrown if the actual value does not implement IEnumerable.

Usage

Is.SubsetOf(IEnumerable expected)

Modifiers

.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 CollectionSubsetConstraint_Examples()
{
    int[] superset = { 1, 2, 3, 4, 5 };

    Assert.That(new[] { 1, 3 }, Is.SubsetOf(superset));       // Passes
    Assert.That(new[] { 1, 2, 3, 4, 5 }, Is.SubsetOf(superset)); // Passes (equal sets are subsets)
    Assert.That(new int[] { }, Is.SubsetOf(superset));        // Passes (empty set is subset of any set)
    Assert.That(new[] { 1, 6 }, Is.Not.SubsetOf(superset));   // Passes (6 not in superset)

    // Case-insensitive string comparison
    string[] colors = { "Red", "Green", "Blue" };
    Assert.That(new[] { "red", "blue" }, Is.SubsetOf(colors).Using((IEqualityComparer<string>)StringComparer.OrdinalIgnoreCase));
}

Notes

  1. A set is always a subset of itself.
  2. The empty set is a subset of every set.
  3. Duplicate items are considered: {1, 1} is a subset of {1, 1, 2} but not of {1, 2}.

See Also