I ran into this odd problem recently working with some Linq2SQL based persistence code.  There is some code someone put together to commit a list of changed entities to the database as part of a single transaction, which simply iterates through the list and performs the appropriate action.  The problem I was having was that I had an object referenced by another object that needed to be persisted first, otherwise there was a foreign key violation.  To add to the strangeness there seemed to be some magic going on (most likely utilizing the INotifyPropertyChanged goodness), so that even if I tried to persist just my dependent object first, both were still showing up in the list, and always in exactly the wrong order.  Now, I’m okay with magic.  Magic makes a lot of things a lot easier.  The problem arises whenever the magic is incomplete, and doesn’t follow through to take care of all of the operation.  Its like someone comming up to you and saying “Pick A Card”, at which point you do, and put the card back, and they say “I know what your card was” and walking away.  Not real convincing.  This is what was going on here.  There was the smarts to know that changes were being made to more than one entity, and there were even attributes to define what properties contained dependent objects, but no smarts to actually deal with a case when you would want to save more than one object in an object graph at a time.

So it occued to me I should be able to do some linqy magic and create some sort of iterator that would return dependent objects in the appropriate order, so the lest dependent of the objects get move to the beginning of the list.  My first step, since I wasn’t really sure how to do this, was to write a test.  And I made it more or less mirror the issue I was facing, a list of two items, one of which is a dependency of the other.  I don’t know if there is a lot of value in posting all of the test cases here, but the end result was rather nice.  Sure it took several iterations, and there was plenty of infinite looping and stack overflows (which does some fun things to studio when your running your tests with TestDriven.Net), but I think this is a reasonable solution to the problem:

public static IEnumerable<T> EnsureDependenciesFirst<T>(this IEnumerable<T> items, Func<T ,IEnumerable> selector)
    if(items.Count() < 2)
    var firstPass = items.SkipWhile(t => items.Intersect(selector(t)).Count() > 0);
    var remainingItems = items.Except(firstPass);
    if(items.Count() == remainingItems.Count())
        return remainingItems;
    return firstPass.Concat(remainingItems.EnsureDependenciesFirst(selector));

Ok, so what do we have here?  Well to start out I’m checking the item list to see if there are at least two items in it, if not I just return the list.  This provides a means to avoid an infinate loop due to the recursive call, and provides a shortcut for a scenario with only one item.  Next off I use the SkipWhile() method, combined with the user-supplied selector function to iterate through each item, retrieve it’s list of dependencies (which is what the selector function does), and checks to see if the current list contains any of the dependencies for the object.  The results of this first pass are the objects which have no dependencies at all, so therefore they need to be first in the list.  The next logical step is to run the operation again for a list that does not contains the items filtered out by the first pass.  This is done via a recursive call back to the EnsureDependenciesFirst extension.  You will notice we’re checking the count of the remaining items against the current list, and returning the list if they are the same.  This is another safety precaution for dealing with infinite loops.  If we have a circular dependency, this bit will just return the items that are interdependent.

You will note that this is a generic function that has really noting at all to do with the entities that I am dealing with.  This was largely due to the fact that this was built TDD, so I just used a simple class which had a property that could take another instance of itself.  To use this to overcome my entity committing problem, I would have to write a not too small function to retrieve the list of dependent objects from the entity (since there would need to be some reflection magic to look at attributes on the properties to determine which properties contain dependencies), but it pretty much will drop in to the foreach statement that is currently being used to persist the entities.

Incidently, I learned from my dev team what the “official” way of dealing with this is a “ReorderChanges” method, which takes two entities, in the order in which they should be persisted.  I think I like my solution better, mostly because it should mean I don’t have to worry about it again.

As of today I have updated several things on the site.  First, I have a new hosting provider, WinHost.  This was primarily a financial decision (saving $3.03 a month, not a lot but hey, every little bit helps, right?), but it looks like there are some nice technical advantages to switching as well.  Some of these are things like IIS 7 hosting, and SQL Server access.  Also you get unlimited domain name pointers, so the IThinkIn.Net domain that I registered a few years back and could never wire up is now live.  While I was in the process of moving to a new server I also updated to the latest version of dasBlog, seeing as I was still running the original .Net 2.0 version from sometime in early 2006 (I think).  I’m not sure whether there will be any immediate signs of new and exciting things, but you never know.  You should now be able to utilize Gravatar icons, and OpenID, so it can’t be all bad right?

Please contact me if for any reason there is an issue with any of the content.  As far as I know everything moved over without a hitch, but I’ve not verified everything at this point.

I was pleased to find recently that Roy Osherove’s Art of Unit Testing was available on Safari.  I have been following Roy’s blog for a while now, and was quite excited at the prospect of him writing a book on Unit Testing.  It was only my personal cheapness that kept me from shelling out the $25 to get the E-Book version from Manning ahead of time.  I have to say, now that I have read it, that it would have been well worth the money.  Before I get too deep I want to provide some context for what I am about to say.

I consider myself an experienced TDD practitioner and Unit Test Writer
So that means that I was reading this book hoping to gain some insight.  I wanted to find out how to write better, more readable, more maintainable tests.  I was also hoping for a little bit of “atta-boy” affirmation that the way I do things is the “right” way.  The astute reader may be able to tell that in order for my first hope to be true, the second may have to get some points taken away.  This was in fact the case, and to be honest, coming out of it I feel like I’ve gotten more value from the things I’ve learned than I received from whatever ego stroking may have occurred with what I am currently doing right.

So lets get started….
I was expecting the book to start out essentially as it did, some brief history about the author and an introduction to Unit Testing for those who may not be familiar with it.  I have to say I was expecting the book to be a little more TDD-centric than it was, but I think most of that was my own bias for TDD as “The Only Way To Write Software”.  Roy actually explained what TDD was, and also why he wasn’t going to harp too much on it throughout the book.  I have to say, I can see why he made the decision that he did.  I can also say that it seemed perfectly clear to me that TDD is a technique that he feels has a lot a value, which made me happy.  Since this is supposed to be a review from the perspective of an experienced practitioner of TDD and Unit Testing, I’m not going to go into anything that was touched on in the early chapters, apart from noting that they contained a general introduction to the tools, technique and philosophy of unit testing.  I can also say that, though I was already familiar with the material, I didn’t mind reading through it at all.  Overall, Roy’s writing style was light and quite pleasant, even for a technical book.

And now into the meat of the book…
For me, things started getting interesting in Part 3 of the book.  This is where issues of test design and organization are addressed.  This is one of those areas that I feel like I need some guidance on, mostly because I developed my testing idioms mostly through habit, and trial and error.  I look back on tests I have written in the past (which could be as little as two days ago) and I wonder how I could have come up with such a brittle, unmaintainable nightmare.  I feel like I need guidance from the experts on what I can do better when writing my tests.  Roy delivered on these items in chapter 7 “The pillars of good tests”.  One of the lessons I took away from this was the value in testing one concept per test.  I had heard this as “one assert per test” in the past, and scoffed at the idea.  But Roy presents a very compelling argument for why this is a good idea, if you are testing multiple concepts, you don’t know the extent of the problem when your test fails.  And lets face it, the failing test is the reason we’re doing this whole thing.  I’ve seen personally the failing test that just keeps failing.  You tackle the issue from one failed assert only to rebuild, and find one right after it which fails as well.  One of the issues I’ve had with this is the redundant setup and configuration that could be required for exercising this concept, but this issue is also addressed by the straight forward recommendation of creating clear and understandable configuration methods.  In the past I have generally not been really good about applying DRY to my test setup, which, I know, is another case of treating tests differently from regular code.  Having someone in a position of authority (like Roy) say, “put your setup in separate methods so you can re-use them and make your tests more readable” made it okay to do the thing that I knew I should be doing anyway.  The key concepts covered are making tests readable, maintainable, and an accurate portrayal of the authors intent.

Even more in depth….
Section 4 goes even further and talks about how to integrate unit testing into an organization which is not already doing it.  This is an interesting subject to me as I have recently moved to a company which has not been doing unit testing and TDD as part of their regular development process.  Roy draws on his experiences as a consultant to provide some really good advice for how to go about enacting this sort of change in an organization.  I particularly pleased with his candor when he describes his failed attempts at integrating unit testing.  It would have been quite easy to simply say “Based on my considerable expertise, these are the things you need to do”, but he chooses instead to share some real-world experience in a straight forward way that only adds to my respect for him as a professional.  In addition to this, he touches on techniques for integrating testing into “legacy” code (i.e. code which is not tested).  He does a good job at introducing some techniques for testing what is essentially untestable code, which a very large nod at Michael Feathers’ “Working Effectively with Legacy Code”.

The book ends with three appendices, one discussing the importance of testability in the design process, one listing vairous testing tools (both Java and .Net), and the last listing guidelines for conducting test reviews.  This last one is nice, because it presents a concise view of all of the guidelines presented throughout the book, and provides page references where you can get the “why” behind each. 

All in all…
This is a really good book, which should be part of any agile development library.  It doesn’t matter if you are writing your first unit tests, or you’re a seasoned pro, there is going to be something here for you.  I think it is great that Roy has chosen to share his experience with the developer community in this way.  I came into this book with some rather high expectations and I think they were met.

A note on TypeMock….
I remember seeing some criticism floating around on twitter suggesting the book was rather pro TypeMock.  There was also the comment that Roy’s affiliation with TypeMock was not made clear early on.  I can’t say I saw either of these things when I was reading it.  For starters, I already knew Roy worked for TypeMock, so perhaps that skewed my ability to objectively judge if the disclosure was done in a timely manner or not.  I can say that the places in the book which there seemed to be a preference for TypeMock were places where he stated things like “I feel TypeMock has a better syntax in this case”, or “TypeMock is the only tool with provides these capabilities”.  For starters, the first is a statement of preference.  Sure Roy helped design the API for TypeMock, so it seems only natural that he would prefer it to other frameworks, but having used it I would have to agree with the statement.  It is a great API, and example if a fluent interface done well.  The second comment is also plain fact.  Of the mocking libraries available in the .Net space, TypeMock is the only one that allows you to swap instances of objects in place, without making changes to the classes using them.  You can argue over whether or not this is a good or a bad thing, but the fact remains that it is a feature specific to TypeMock.  Maybe I was expecting something more blatant and obvious, but I just didn’t see it.