Question

I have the following method

    public void ValidateAccessToFile(string filePath, List<String> errorMessageList)
    {
        try
        {
            using (FileStream fs = (FileStream)_iomgr.OpenFile(filePath))
            {
                if (fs.CanRead && fs.CanWrite) { }
                else
                {
                    errorMessageList.Add("Can not read/write to the specified file.");
                }
            }
        }
        catch (Exception e)
        {
            errorMessageList.Add(e.Message);
        }
    }

and id like to test that it writes to the “errorMessageList” if either of the properties, CanRead or CanWrite are false. Is this possible?

    [Test]
    public void ValidateAccessToFile_CanReadWriteToFile_NoErrorAddedToErrorListMessage()
    {
        Mock<IIOManager> mock = new Mock<IIOManager>();
        mock.Setup(x => x.OpenFile(It.IsAny<string>())).Returns(new MemoryStream());

        List<String> errorMessageList = new List<string>();

        VerificationManager testObject = new VerificationManager(mock.Object);
        testObject.ValidateAccessToFile("Random.txt", errorMessageList);
        Assert.AreEqual(errorMessageList.Count, 0);
    }

How can i assign a value to the New MemoryStream properties?
Thanks for your time.

EDIT

Below is the final test method i wrote.

    public void ValidateAccessToFile_CanReadWriteToFile_NoErrorAddedToErrorListMessage()
    {
        bool _isReadOnly = true;
        List<String> errorMessageList = new List<string>();

        Mock<IIOManager> mock = new Mock<IIOManager>();
        mock
            .Setup(x => x.IsReadOnly(It.IsAny<string>()))
            .Returns(_isReadOnly);

        VerificationManager testObject = new VerificationManager(mock.Object);
        testObject.ValidateAccessToFile(It.IsAny<string>(), errorMessageList);
        Assert.AreEqual(errorMessageList.Count, 0);
    }

Answer 1

According to the documentation for MemoryStream.CanRead, the property will always return true as long as the stream is open. (CanWrite is less clear, but I believe it is the same.)

So, you can close the stream before returning it, or you can mock a Stream with the appropriate overrides.

Incidentally, I’m not sure that a MemoryStream can be casted into a FileStream. See this post.