public void ReadLine()
        {
            var service = new InMemoryInteractiveService();

            service.StdInWriter.WriteLine("Line 1");
            service.StdInWriter.WriteLine("Line 2");
            service.StdInWriter.WriteLine("Line 3");
            service.StdInWriter.Flush();

            Assert.Equal("Line 1", service.ReadLine());
            Assert.Equal("Line 2", service.ReadLine());
            Assert.Equal("Line 3", service.ReadLine());

            service.StdInWriter.WriteLine("Line 4");
            service.StdInWriter.WriteLine("Line 5");
            service.StdInWriter.WriteLine("Line 6");
            service.StdInWriter.Flush();

            Assert.Equal("Line 4", service.ReadLine());
            Assert.Equal("Line 5", service.ReadLine());
            Assert.Equal("Line 6", service.ReadLine());
        }
        public void ReadLineSetToNull()
        {
            var service = new InMemoryInteractiveService();

            Assert.Throws <InvalidOperationException>(() => service.ReadLine());
        }