[Test]
        public void CollectionSubsetConstraint()
        {
            ///CollectionSubsetConstraint tests that one IEnumerable is a subset of another.
            ///If the actual value passed does not implement IEnumerable, an exception is thrown.

            //Syntax: Is.SubsetOf(IEnumerable)

            //arrange
            int[] iarray = new int[] { 1, 3 };

            //act

            //assert
            Assert.That(iarray, Is.SubsetOf(new int[] {1, 2, 3 }));
        }