ExactCount Constraint

ExactCountConstraint tests that an IEnumerable contains exactly a specified number of items that match an optional constraint. An exception is thrown if the actual value does not implement IEnumerable.

Usage

Has.Exactly(int count).Items
Has.Exactly(int count).<constraint>

Examples

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

    // Count total items
    Assert.That(numbers, Has.Exactly(5).Items);
    Assert.That(names, Has.Exactly(3).Items);

    // Count items matching a constraint
    Assert.That(numbers, Has.Exactly(2).GreaterThan(3));       // 4 and 5
    Assert.That(numbers, Has.Exactly(3).LessThanOrEqualTo(3)); // 1, 2, and 3
    Assert.That(names, Has.Exactly(1).Length.EqualTo(3));      // "Bob"

    // Combining multiple counts
    Assert.That(numbers, Has.Exactly(2).LessThan(3).And.Exactly(2).GreaterThan(3));

    // Zero items matching
    Assert.That(numbers, Has.Exactly(0).LessThan(0));          // No negatives
}

Notes

  1. The Items keyword is required when counting total items (no constraint). It's optional when a constraint follows.
  2. Has.Exactly(0) is useful for asserting that no items match a condition.
  3. For simple count/length checks, consider using PropertyConstraint with Has.Count or Has.Length.

See Also