Being Cellfish

Stuff I wished I've found in some blog (and sometimes did)

June, 2008

Change of Address
This blog has moved to blog.cellfish.se.
Posts
  • Being Cellfish

    Code Coverage

    • 3 Comments

    Measuring code coverage is often perceived as a good measure of test quality. It is not. Good tests finds problems when changes are made to the code. But if you just want to have large code coverage you can easily make a number of tests calling all your methods but not checking the results. The only thing high code coverage values really tell you is that the code is at least not crashing with the given input.

     

    If you however are using BDD/TDD, code coverage values might be of interest. For example if you do not have 100% function coverage (i.e. not 100% of the functions are called) then you aren't really using BDD/TDD are you? Because how could you write a method that is not called by anyone? Well actually you might have created methods that are never called by your tests. Many TDD practitioners use a rule "to simple to test" which applies to real simple, property like methods. I don't really like that philosophy, but more on that in a later post.

     

    So now you think with 100% function coverage you will also have 100% line coverage with BDD/TDD, right? Well, yes and no. Typically you don't since you will add error handling with logging methods that will never occur since the errors never occur in your tests. It might be that you open a file and if that fails you log an error and exit your application. This never happens in the tests since you always manage to open the file in your tests. So how did those lines get in there if never called? Well one other rule often used by TDD practitioners is that you "should not do stupid things". If a system call may fail, you check the result regardless of tests or not. With dependency injection you'll probably get close to 100% but there is no point in bending back-wards in order to achieve high code coverage.

     

    Does this mean there is no point in measuring code coverage? I think it is great to measure code coverage if you use the result correctly. You should not add more tests just to increase coverage since test added just to increase coverage tend to just exercise code and not really testing something interesting. But low code coverage when using BDD/TDD is definitely a warning signal that something is wrong. The team is not using the methodology correctly. So what is considered OK coverage levels? From personal experience I think anything below the levels listed in the table below should be considered bad since type without injectiontype withoutinjection with with you should have no problem at all achieving the given values.
     

    Coverage type without dependency injection with dependency injection
    Function 90% 99%
    Line 75% 95%

    But sometimes there is someone (usually a manager) that thinks coverage should be above some level. So even though you know those tests will not really be useful you have to add more tests for coverage. What do you do? Either you can try to ignore the coverage fact and just try to add more tests, testing interesting things. Or you could try using Pex. Pex is a tool from Microsoft Research that is an automated exploratory testing tool. It can be used to make a small test suite with high code coverage and with only a few simple examples I get the impression it is quite good at finding border cases in your code. This will not however replace your traditional tests/specifications written as part of your TDD/BDD process. But it can help you test some cases you did not think of and that way increase code coverage even more without any extra effort from you. At least it is better than adding coverage tests by hand.

  • Being Cellfish

    Readable SQL

    • 3 Comments

    I read this article on SQL Code Layout and Beautification and can only agree with the author that other people's SQL often is hard to understand because I'm so used to how I write my SQL statements. One of the links is to an on-line tool formatting your SQL according to a number of rules. I was happy to find that my way of writing SQL was supported:

    SELECT a,
           b,
           c AS d
      FROM x,
           y,
           z AS w
     WHERE a = 2
       AND b IN (3,4,7)

    And another example:

      SELECT obj.run,
             obj.camcol,
             STR(obj.field,3) AS field,
             STR(obj.rowc,6,1) AS rowc,
             STR(obj.colc,6,1) AS colc,
             STR(dbo.FOBJ(obj.objid),4) AS id,
             STR(obj.psfmag_g - 0 * obj.extinction_g,6,3) AS g,
             STR(obj.psfmag_r - 0 * obj.extinction_r,6,3) AS r,
             STR(obj.psfmag_i - 0 * obj.extinction_i,6,3) AS i,
             STR(obj.psfmag_z - 0 * obj.extinction_z,6,3) AS z,
             STR(60 * distance,3,1) AS d,
             dbo.FFIELD(neighborobjid) AS nfield,
             STR(dbo.FOBJ(neighborobjid),4) AS nid,
             'new' AS 'new'
        FROM (SELECT obj.objid,
                     run,
                     camcol,
                     field,
                     rowc,
                     colc,
                     psfmag_u,
                     extinction_u,
                     psfmag_g,
                     extinction_g,
                     psfmag_r,
                     extinction_r,
                     psfmag_i,
                     extinction_i,
                     psfmag_z,
                     extinction_z,
                     nn.neighborobjid,
                     nn.distance
                FROM photoobj AS obj
                     JOIN neighbors AS nn
                       ON obj.objid = nn.objid
               WHERE 60 * nn.distance BETWEEN 0 AND 15
                 AND nn.mode = 1
                 AND nn.neighbormode = 1
                 AND run = 756
                 AND camcol = 5
                 AND obj.TYPE = 6
                 AND (obj.flags & 0x40006) = 0
                 AND nchild = 0
                 AND obj.psfmag_i < 20
                 AND (g - r BETWEEN 0.3 AND 1.1
                      AND r - i BETWEEN -0.1 AND 0.6)) AS obj
             JOIN photoobj AS nobj
               ON nobj.objid = obj.neighborobjid
       WHERE nobj.run = obj.run
         AND (ABS(obj.psfmag_g - nobj.psfmag_g) < 0.5
               OR ABS(obj.psfmag_r - nobj.psfmag_r) < 0.5
               OR ABS(obj.psfmag_i - nobj.psfmag_i) < 0.5)
    ORDER BY obj.run,
             obj.camcol,
             obj.field

  • Being Cellfish

    How to set up an agile work space

    • 1 Comments
    I stumbled across this video with a tour of the Patterns & Practices team at Microsoft. I think it shows pretty good how you can create a good team work space. Spanning from occupying conference rooms to rebuilding your office for a million dollars to match your needs. Pretty inspiring I think. And since a picture says more than a thousand words I guess this 15 minute clip will say pretty much...
  • Being Cellfish

    C# source analysis

    • 0 Comments
     

    And if you listened to me and started to write nice looking SQL, maybe you wanna look ate making your C# code look nice too...

  • Being Cellfish

    Constraints - when user stories don't do it for you

    • 0 Comments

    In "agile projects" it is common to use user stories to describe what has to be done. But it is also common to use constraints to describe things that cannot be described in a user story. This can be things like:

    • Response times should always be less than one second.
    • We should always apply coding standards in document XXX.

    Constraints are things that should always be considered during every user story implemented.

     

    However sometimes people come along with things that sound like constraints but they're not. For example:

    • We should spend up to 10% of the velocity on improving performance.

    This is a bad constraints since it have no goal. You might think you improve the constraint if you say:

    • We should spend up to 10% of the velocity on improving performance until all response times are less than one second.

    This is still a bad constraint since you probably have a release date. What happens if the constrained time is not enough to achieve the goal?

     

    I think that if there is a known problem (for example some responses take more than one second) you should add user stories (or bugs) for that and prioritize and plan the fixes for those problems just like anything else. And if you have no known problems you should just set up constraints telling the team what kind of quality you want. If it takes the team 50% of the velocity to pass all the constraints you should let them do so since otherwise you'll have to let them do it later anyway. Either way you'll notice the team are struggling to pass all the constraints and maybe they are to strict. But if you time box them from the start you will notice this later than if you force the team to always deliver more or less release quality.

  • Being Cellfish

    Nothing is "Too simple to test"

    • 0 Comments
    A common practice taught in many TDD classes is the principle of too easy to test. The principle basically says that you should not test really simple things since then you will spend time writing tests that not really add value.

     

    This is a fair recommendation and actually makes a lot of sense. Especially if you're implementing TDD in a team where people are a little bit skeptical. But there are a few dangers with allowing the use of this rule.

    • Exactly what is considered too easy to test may be different if you ask different developers. Those who are reluctant to embrace TDD tend to stretch this line quite far.
    • If something that once was really simple and then didn't need a test later on is changed to something more complex there is a risk that the developer will not add a new test since there was no tests before.

    Personally I think that if something is considered to be so simple it does not need a test, it must be really simple to test. And if it so simple to test why shouldn't you use it. The relative cost might be high but the absolute cost for adding a real simple test for some real simple functionality is worth it in my book since it removes the decision from the developer. "No new functionality unless you have failing tests" is much simpler to follow and remember than "no new functionality unless you have failing tests or you consider the functionality to be really simple". Also consider the code coverage issues.

  • Being Cellfish

    Use OneNote 2007 to make screen shots

    • 0 Comments
    The more I use OneNote 2007, the more I like it. I find the possibility to share notebooks and also working offline with a notebook on a server very useful. But one of the really nice things is when you have to make a screen shot. Previously I've been using the PrintScrn-button (with or without Alt) and then cropped the screen shot to what I need in some application like paint. But with OneNote I don't have to do that any more. With OneNote installed I just have to hit "WindowsLogoKey-S" and the screen is dimmed. I use the mouse to draw a rectangle of what I need captured from the screen and the image is pasted into my OneNote, ready to be used.
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