C# Code Contracts and Interface Properties, http://d-fens.ch/2016/05/22/c-code-contracts-and-interface-properties

ContractTest.cs

/**
 * Copyright 2016 d-fens GmbH
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
using System.Runtime.CompilerServices;
using biz.dfch.CS.Utilities.General;
using System;
using System.Collections.Generic;
using System.Diagnostics.Contracts;
using System.IO;
using System.Linq;
using System.Management.Automation;
using System.Web;
using System.Collections;

namespace biz.dfch.CS.General.Tests
{
    public class ContractTest : IContractTest
    {

        public int NonZeroNumber { get; set; }

        [ContractInvariantMethod]
        private void ContractInvariantMethod()
        {
            Contract.Invariant(0 != NonZeroNumber);
        }

        private string _NonEmptyString;
        public string NonEmptyString
        {
            get 
            {
                Contract.Ensures(string.IsNullOrEmpty(Contract.Result<string>()));

                return _NonEmptyString; 
            }
            set 
            {
                Contract.Requires(string.IsNullOrEmpty(value));

                _NonEmptyString = value; 
            }
        }

        public ContractTest(int i)
        {
            NonZeroNumber = 0; ///< will not violate contract
            NonZeroNumber = i;
        }

        public ContractTest(string s)
        {
            NonEmptyString = string.Empty; ///< will violate contract
            NonEmptyString = s;
        }

    }
}

ContractTestTest.cs

/**
 * Copyright 2016 d-fens GmbH
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
using System.IO;
using System.Reflection;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Management.Automation;

namespace biz.dfch.CS.General.Tests
{
    [TestClass]
    public class ContractTestTest
    {
        [TestMethod]
        public void ContractInvariantSucceeds()
        {
            // Arange
            var i = 42;

            // Act
            var sut = new ContractTestTest(i);

            // Assert
            Assert.AreEqual(i, sut.NonZeroNumber);
        }

        [TestMethod]
        [ExpectContractFailure]
        public void ContractInvariantThrowsContractException()
        {
            // Arange
            var i = 0;

            // Act
            var sut = new ContractTestTest(i);

            // Assert
            // N/A
        }

        [TestMethod]
        [ExpectContractFailure]
        public void ContractBodyThrowsContractException()
        {
            // Arange
            var s = "arbitrary-non-empty-string";

            // Act
            var sut = new ContractTestTest(s);

            // Assert
            // N/A
        }

    }
}