public void TestMultiply()
        {
            var c      = new MockCalculator(_resultWriter);
            var result = c.Multiply(3, 2);

            Assert.Equal(result, 6);
        }
        public void TestException()
        {
            var mock = new Mock <IResultWriter>();

            mock.Setup(o => o.WriteResult(It.IsAny <double>())).Throws(new IOException("Disk is full"));

            var c = new MockCalculator(mock.Object);

            Assert.Throws <IOException>(() => c.Multiply(3, 2));
        }