MsTest中实现类似NUnit中Assert.Throws

      我们做单元测试NUnit中,有一个断言Assert.Throws很好用,但当我们使用MsTest时你需要这样写:

        [TestMethod]
        [ExpectedException(typeof(ArgumentNullException))]
        public void WriteToTextFile()
        {
            PDFUtility.WriteToTextFile("D:\\ACA.pdf", null);
        }

     现在让我们来扩展一下也实现类似成功能,增加一个类,代码如下:

    /// <summary>
    /// Useful assertions for actions that are expected to throw an exception.
    /// </summary>
    public static class ExceptionAssert
    {
        /// <summary>
        /// Executes an exception, expecting an exception to be thrown.
        /// Like Assert.Throws in NUnit.
        /// </summary>
        /// <param name="action">The action to execute</param>
        /// <returns>The exception thrown by the action</returns>
        public static Exception Throws(Action action)
        {
            return Throws(action, null);
        }

        /// <summary>
        /// Executes an exception, expecting an exception to be thrown.
        /// Like Assert.Throws in NUnit.
        /// </summary>
        /// <param name="action">The action to execute</param>
        /// <param name="message">The error message if the expected exception is not thrown</param>
        /// <returns>The exception thrown by the action</returns>
        public static Exception Throws(Action action, string message)
        {
            try
            {
                action();
            }
            catch (Exception ex)
            {
                // The action method has thrown the expected exception.
                // Return the exception, in case the unit test wants to perform further assertions on it.
                return ex;
            }

            // If we end up here, the expected exception was not thrown. Fail!
            throw new AssertFailedException(message ?? "Expected exception was not thrown.");
        }

        /// <summary>
        /// Executes an exception, expecting an exception of a specific type to be thrown.
        /// Like Assert.Throws in NUnit.
        /// </summary>
        /// <param name="action">The action to execute</param>
        /// <returns>The exception thrown by the action</returns>
        public static T Throws<T>(Action action) where T : Exception
        {
            return Throws<T>(action, null);
        }

        /// <summary>
        /// Executes an exception, expecting an exception of a specific type to be thrown.
        /// Like Assert.Throws in NUnit.
        /// </summary>
        /// <param name="action">The action to execute</param>
        /// <param name="message">The error message if the expected exception is not thrown</param>
        /// <returns>The exception thrown by the action</returns>
        public static T Throws<T>(Action action, string message) where T : Exception
        {
            try
            {
                action();
            }
            catch (Exception ex)
            {
                T actual = ex as T;
                if (actual == null)
                {
                    throw new AssertFailedException(message ?? String.Format("Expected exception of type {0} not thrown. Actual exception type was {1}.", typeof(T), ex.GetType()));
                }

                // The action method has thrown the expected exception of type 'T'.
                // Return the exception, in case the unit test wants to perform further assertions on it.
                return actual;
            }

            // If we end up here, the expected exception of type 'T' was not thrown. Fail!
            throw new AssertFailedException(message ?? String.Format("Expected exception of type {0} not thrown.", typeof(T)));
        }
    }

好了,现在我们在MsTest中可以这样了,看下面代码:

        [TestMethod]
        public void WriteToTextFile2()
        {
            //Implement Assert.Throws in MSTest
            ExceptionAssert.Throws<ArgumentNullException>(()=> PDFUtility.WriteToTextFile("D:\\ACA.pdf", null)
                ,"Output file path should not be null");

        }

看上去是不是感觉很COOL. 希望这篇文章对您做单元测试有帮助.

作者：Petter Liu
出处：http://www.cnblogs.com/wintersun/
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