Question

I have a method that serializes a collection to a file using the XmlSerializer.

    public void Save(List<RetryAttempt> retryAttempts)
    {
        FileStream fs = new FileStream(this.fileName, FileMode.Create);

        try
        {
            XmlSerializer xmlSerializer = new XmlSerializer(typeof(List<RetryAttempt>));
            xmlSerializer.Serialize(fs, retryAttempts);
        }
        catch (Exception ex)
        {
            LocalLogger.LogError("Unable to save retry information to xml file.", ex.ToString());
        }
        finally
        {
            fs.Close();
        }
    }

I then have another method that deserializes the collection back from the file

    public List<RetryAttempt> GetRetryAttempts()
    {
        List<RetryAttempt> retryAttempts = new List<RetryAttempt>();

        if (File.Exists(this.fileName))
        {
            FileStream fs = new FileStream(this.fileName, FileMode.Open);

            try
            {
                XmlSerializer xmlSerializer = new XmlSerializer(typeof(List<RetryAttempt>));
                retryAttempts = (List<RetryAttempt>)xmlSerializer.Deserialize(fs);
            }
            catch (Exception ex)
            {
                LocalLogger.LogError("Unable to read from retry xml file.", ex.ToString());
            }
            finally
            {
                fs.Close();
            }
        }

        return retryAttempts;
    }

So far so good (unless anyone spots something glaringly wrong with that code…). However, my unit test for this now fails

    [Test]
    public void GetRetryAttempts_AttemptsExist_ListOfAttemptsReturned()
    {
        this.attempt = new RetryAttempt("1234", 4);
        this.attempts = new List<RetryAttempt>() { attempt };
        this.xmlStore = new XmlRetryFileStore(RetryType.Download);
        xmlStore.Save(attempts);

        List<RetryAttempt> savedAttempts = xmlStore.GetRetryAttempts();
        Assert.Contains(attempt, savedAttempts);
    }

I would expect the list of my custom object to contain the “attempt” that I serialized to the file. Instead I am getting the following failure.

Expected: collection containing < MyNamespace.RetryManagement.RetryAttempt >
But was: < MyNamespace.RetryManagement.RetryAttempt >

This message seems to suggest that instead of a collection being returned, just one object was returned. This is obviously not the case – there is a List being returned that only contains one element – I can see the collection in the immediate window and everything looks fine. I can run the test with the debugger and everything seems okay. If I simply create a collection and assert that it contains the element without saving and getting it from XML then it works fine so the point of failure must be around the serialization?

Answer 1

I would suspect that your class doesn’t implement its own overridden version of .Equals method. The contains method would otherwise do a reference check and since you are comparing serialized versions with the original the instances are not the same.

I would suggest implementing this (along with GetHashCode so you are able to do comparisons for equality