Range Constraint

RangeConstraint tests that a value falls within an inclusive range. Both the lower and upper bounds are included in the valid range.

Usage

Is.InRange(IComparable from, IComparable to)

Modifiers

.Using(IComparer comparer)
.Using<T>(IComparer<T> comparer)
.Using<T>(Comparison<T> comparer)

Examples

[Test]
public void RangeConstraint_Examples()
{
    // Numeric ranges (inclusive)
    Assert.That(5, Is.InRange(1, 10));
    Assert.That(1, Is.InRange(1, 10));   // Lower bound is included
    Assert.That(10, Is.InRange(1, 10));  // Upper bound is included
    Assert.That(0, Is.Not.InRange(1, 10));

    // DateTime ranges
    var start = new DateTime(2024, 1, 1);
    var end = new DateTime(2024, 12, 31);
    Assert.That(new DateTime(2024, 6, 15), Is.InRange(start, end));

    // String ranges (alphabetical comparison)
    Assert.That("banana", Is.InRange("apple", "cherry"));
}

Notes

  1. The range is inclusive on both ends: Is.InRange(1, 10) passes for values 1, 10, and everything in between.

  2. from must be less than or equal to to, otherwise the constraint throws an ArgumentException. Negative bounds are fine, but the range must be written in increasing order: use Is.InRange(-10, 0), not Is.InRange(0, -10). If the bounds are computed and could end up in either order, sort them first:

    int lower = Math.Min(a, b);
int upper = Math.Max(a, b);
Assert.That(actual, Is.InRange(lower, upper));

  3. For exclusive bounds, combine Is.GreaterThan and Is.LessThan with And:

    Assert.That(5, Is.GreaterThan(1).And.LessThan(10));  // Exclusive bounds

  4. RangeConstraint has no Within modifier. To allow for imprecision, widen the bounds, or combine Is.GreaterThan and Is.LessThan with their own tolerances.

See Also