Proven strategies for maintaining and optimizing legacy code to get the most out of your existing applications. Articles What is this concept good for? Home The db_update function talks directly to a database. To me, the answer is straightforward, and it is a point that I elaborate throughout the book: Code without tests is bad code. Where is the enabling point? Let's take a look at the example We can do it because the #include directive of the C preprocessor gives us a seam that we can use to replace text before it is compiled. The compiler then emits object code or bytecode instructions. In most programming environments, program text is read by a compiler. You issue calls to functions to tell them to do something, and you aren't asking for much Regardless of which scheme your language uses to resolve references, you can usually exploit it to substitute pieces of a program. We can create a library with a stub function and link to it to get rid of the behavior. If we delete the keyword static on Recalculate and make it a protected method instead of a private method, we can subclass and override it during test: Isn't this all rather indirect? Yes. Only a couple of languages have a build stage before compilation. It sure looks like just a sheet of text, doesn't it? Analytics cookies. In addition, tests that depend upon them can be hard to maintain. Is there an object seam at the call to Recalculate in this version of buildMartSheet? We are using this new method to delegate to the global PostReceiveError function using C++'s scoping operator (::). Thinking in terms of “seams” can help you identify stronger methods of dynamic behavior modification. When we are lucky, the dependencies In C and C++, a macro preprocessor runs before the compiler. > Programming. The types of seams available to us vary among programming languages. Sometimes it is in a build or a deployment script. I'm reading "Working Effectively with Legacy Code", and was thinking about the "fancy" seams that he discusses in Chapter 4. Object seams are available in object-oriented languages, and they are only one of many different kinds of seams. We could add a #include statement to the code and use the preprocessor to define a macro named PostReceiveError when we are testing. Articles Although it would be confusing to use this trick in production code, when you are testing, it can be a pretty handy way When TESTING is defined, the localdefs.h file defines macros that replace calls to db_update in the source file. Use features like bookmarks, note taking and highlighting while reading Working Effectively with Legacy Code … Shop now. The idea of a program as a sheet of text just doesn't cut it anymore. Where would the seam be? When we are lucky, the dependencies that we have are small and localized; but in … Often the easiest way to use the link seam is to We have a little indirection there, but we end up calling the same global function. WORKING EFFECTIVELY WITH LEGACY CODE. Home … Where is the enabling point? The Recalculate method is a static method. each of the calls so that you can have a complete program at runtime. In this example, the enabling point is the argument list of buildMartSheet. define named TESTING. Changing Messy Software Without Breaking It. In the previous example, we wanted to change the They resolve Suppose we wanted to supply a different version of the Parse class for testing. The analogy is a seam … Interestingly a type is a good choice: The case of a graphics library is a little atypical. Here is an example of some typical code: This code makes many direct calls to a graphics library. > If we can replace behavior at The conditional Often a code that indicates success or the default value of We can't really go to that place and change the code just Separation is often a reason to use a link seam. Save 70% on video courses* when you use code VID70 during checkout. Working Effectively with Legacy Code is the logical culmination of Refactoring and Test Driven Development 4 (TDD); it's where the rubber meets the road when combining unit testing and refactoring. If the class hasn't been compiled, August 2004; ... A seam is a part of the code that can be isolated and work alone in separation from the rest of the codebase [13]. This can be a bit of work, but it can pay off if you > But not all So the Building seams into your code enables separating the piece of code under test, but … The "seam" model of thinking, where you identify points you can influence behaviour without changing the code, is extremely powerful. Object seams are pretty much the most useful seams available in object-oriented programming languages. No. Examples in C-sharp, C++, and Java, as well as strategies for better using the industry standard modeling language: UML 2.0 Addresses the very concrete problems that programmers face working in the context of large untested code … … to test it. … To do this, we can introduce a header file called localdefs.h. To exploit that seam, you have to make a change someplace else. seams, we can selectively exclude dependencies in our tests. We can use preprocessing seams to replace the calls to db_update. We want to avoid executing that line of code because PostReceiveError is a global function that communicates with another subsystem, and that subsystem is a pain to work with under test. How do we do that and still allow the call to PostReceiveError in production? that led off this chapter again and see what seams we can see: What seams are available at the PostReceiveError call? The fundamental thing Let's take a look at an example, a function in C++. The enabling point for a link seam is always outside the program text. In this case, the enabling point is a preprocessor Is the call to cell.Recalculate in buildMartSheet a seam now? Is the call to Recalculate in buildMartSheet a seam? that works, but in particularly nasty legacy code, often the best approach is to do what you can to modify the code as little enough, you often have a lot of work to do, regardless of how "good" the design is. I just recently finished Michael Feathers' book Working Effectively with Legacy Code. In languages such as C and C++, there really is a separate linker that does the operation I just described. We'll have ended up varying what the call to cell.Recalculate does without changing the method that calls it. Working Effectively with Legacy Code. languages, the compiler does the linking process behind the scenes. When you get used to seeing code in terms of seams, it is easier to see how to test things and to see how to structure new In the implementation file, we can add a body for it like this: That change should preserve behavior. I didn't mention it earlier, but there is something else that is important to understand about seams: Every seam has an enabling point. Let's look at a Java example: When we look at this code, it seems that there has to be a method named Recalculate that will execute when we make that call. Download it once and read it on your Kindle device, PC, phones or tablets. Seams: Some thoughts. > The purpose of the book is to describe how we can add features, fix bugs and refactor in legacy code … This term was first introduced to me in the book, Working effectively with Legacy Code by Michael Feathers. Macros (defined with #define) can be used to do some very good things, but they just do simple text replacement. So, we have a preprocessing seam there. Preprocessing seams are pretty powerful. In Java and similar of the graphics library we just faked, we could introduce some additional data structures to record calls: With these data structures, we can sense the effects of a function in a test: The schemes that we can use to sense effects can grow rather complicated, but it is best to start with a very simple scheme What happens if we add a method with the exact same signature to the CAsynchSslRec class? One of the biggest challenges in getting legacy code under test is breaking dependencies. ): It's not a good idea to use excessive preprocessing in production code because it tends to decrease code clarity. Here is a little class called FitFilter: In this file, we import fit.Parse and fit.Fixture. Helllo Rainer, as far I am know a statement like TEST-SEAM is not available for other languages. In object-oriented languages, not all method calls are seams. Tips for Working with Legacy Code. library, you can create stub versions that link to the rest of the application. a lot of embedded calls to a graphics library. In many older languages, nearly all linking is static; it happens once after compilation. of breaking dependencies. For instance, imagine a CAD application that contains that we have are small and localized; but in pathological cases, they are numerous and spread out throughout a code base. In the case When you start to try to pull out individual classes for unit testing, often you have to break a lot of dependencies. Working Effectively with Legacy Code (Robert C. Martin Series) - Kindle edition by Feathers, Michael. our makefile or some setting in our IDE. All we have to do is go into the code and delete that line. The class of the cell is decided when the object is One reason that it is a good candidate for this technique is that it Each identifiable step exposes different kinds The seam view of software helps us see the opportunities that are already in the code base. You can do sensing also; it just requires a little more work. It could even be the Recalculate method of some other class that doesn't inherit from Cell (if that's the case, cell was a particularly cruel name to use for that variable!). How should we look at it? Here's the definition of a seam. behavior at the text of the db_update call. Many C and C++ build systems perform static linking to create executables. In general, object seams are the best choice in object-oriented languages. what you want it to do is to look at the computer screen when figures are redrawn. created, and we can't change it without modifying the method. There is no enabling point. compilation directives (#ifdef, #ifndef, #if, and so on) pretty much force you to maintain several different programs in the same source code. Sometimes We'd have to alter our build so that we would link to a testing library when we are The definition of "Legacy Code" given in this book is simple but often shocking to the uninitiated: Legacy Code == Code … Okay, now what if we subclass the CAsyncSslRec class and override the PostReceiveError method? Feathers gives several types of seam, and many techniques for … Working Effectively with Legacy Code Core Concept Best agile practices of cleaning code “on the fly” that will instill within you the values of a software craftsman and make you a better programmer—but only if you work … executed. The best way to explore them is to look at all of the Depending on the programming language there might be comparable techniques to offer a test seam. Suppose that we want to run all of that method except for this line: It's easy, right? To quote the book: A seam … In Java, you can use a classpath environment variable to determine where Why seams? The compiler produces an intermediate representation it compiles it, if necessary, and then checks to see if all of its calls will really resolve correctly at runtime. “Working Effectively with Legacy Code” Summary ... Another useful term is a “seam.” A seam, in this context, is “a place where you can alter behavior in your program without editing in that place.” The analogy is to a seam … One of the biggest challenges in getting legacy code under test is breaking dependencies. Unless we can substitute in another implementation of the routine, we can't sense You can find them in many programming languages. When you do that, you can alter your build scripts Agile Transformation: Using the Integral Agile Transformation Framework to Think and Lead Differently, Mobile Application Development & Programming. Every seam has an enabling point, a place where you can make the decision to use one behavior or another. want to sense conditions in the code and write tests against those conditions. Is the call to Recalculate an object seam? It could be the Recalculate method of ValueCell or the Recalculate method of FormulaCell. We use analytics cookies to understand how you use our websites so we can make them … In C and C++, a macro preprocessor runs before the compiler. We can decide what kind of an object to pass and change the behavior of Recalculate any way that we want to for testing. When you have a seam, you have a place where behavior can change. In this book, Michael Feathers offers start-to-finish strategies for working more effectively with large, untested legacy code bases. The source code should be the same in both production and test. tests in place to support more aggressive work. This makes the use of link seams somewhat hard to notice. C and C++ are the most common of them. Agile Transformation: Using the Integral Agile Transformation Framework to Think and Lead Differently, Mobile Application Development & Programming. A seam is a place where you can alter behavior in your program without editing in that place. We were able to change the method that is called without changing the method that calls it. In most, there is some way to exploit link seams. and allow it to get only as complicated as it needs to be to solve the current sensing needs. This sort of dynamic linking can be done in many languages. as possible when you are getting tests in place. Within it, we can provide a definition for db_update and some variables that will be helpful for us: With this replacement of db_update in place, we can write tests to verify that db_update was called with the right parameters. To me, legacy code is simply code without tests. How do the compiler and the JVM find those classes? An alternative is to use link seams. I talk with Jason Swett about working with legacy code, adding tests to legacy code, how to safely make changes to legacy applications, and more. If all of the drawing functions are part of a particular to recognize is that when we look at a call in an object-oriented program, it does not define which method will actually be In most programming environments, program text is read by a compiler. the behavior of the function. I don't think I'd really want a preprocessor for Java and other more modern languages, Here is a tricky one. When a source file contains an import statement, the compiler checks to see if the imported class really has been compiled. the dependency, they can be just empty functions: If the functions return values, you have to return something. To me, that is a question with many possible answers, and it leads to the idea of a seam. Contribute to ontiyonke/book-1 development by creating an account on GitHub. A seam is a place where you can alter behavior in your program without editing it in that place. We can also nest code in conditional compilation statements like this to support debugging and different platforms (aarrrgh! of the code, and that representation contains calls to code in other files. Without knowing what object cell points to, we just don't know. These considerations aside, I'm actually glad that C and C++ have a preprocessor because the preprocessor gives us more seams. are trying to exercise your code. Yes. I’ve gotten some grief for this definition. We can create a CustomSpreadsheet in a test and call buildMartSheet with whatever kind of Cell we want to use. terribly obscure bugs. Okay, most object seams are pretty straightforward. Shop now. Michael C. Feathers offers a nice definition in Working Effectively with Legacy Code: A seam is a … In many language systems, compilation isn't the last step of the build process. Working Effectively with Legacy Code. steps involved in turning the text of a program into running code on a machine. fact is, there can be more than one: Which method will be called in this line of code? Over the years, the macro preprocessor has been cursed and derided Yes. directory, and alter the classpath to link to a different fit.Parse and fit.Fixture. Asking for information is difficult because the defaults often aren't the right thing to return when you It is easy to create macros that hide linking is dynamic. Only a couple of languages have a build stage before compilation. The terms “Seams” was introduced in popular language by Michael Feathers in his excellent book Working Effectively with Legacy Code as a place where we can alter behavior in a program without editing in that place. Working Effectively with Legacy Code; None; Legacy code is... code that is hard to change; a mess; legacy code doesn’t need to be old; code without tests; ... seams: with different libraries • Object seams Seams • Preprocessing seams… ^^ Michael Feathers, Working effectively with Legacy Code. We don't have to edit buildMartSheet to change behavior at that call. We can get rid of the behavior there in a couple of ways. information back. incessantly. I talk with Robby Russell about practices like feature toggling or sustainability weeks to work … Over the years, the macro preprocessor has been cursed and derided incessantly. We can't change which Recalculate method is called because the choice depends on the class of the cell. Let's list them. It was a great book on how to effectively create test seams and exploit them to get existing code under test. Here is an example of a call that isn't a seam: In this code, we're creating a cell and then using it in the same method. Okay, let's constrain the problem a little more. The compiler then emits object code or bytecode instructions. The seam is the new Parse call in the process method. We can also run other code where those dependencies were if we If we do that and go back to where we are creating our CAsyncSslRec and create a TestingAsyncSslRec instead, we've effectively nulled out the behavior of the call to PostReceiveError in this code: Now we can write tests for that code without the nasty side effect. problem becomes, how do we execute the method without calling PostReceiveError under test? C and C++ are the most common of them. for testing really changes your idea of what "good" is with regard to design. I pick up Michael Feathers’ Working Effectively with Legacy Code book from time to time and one of my favourite parts of the book is the chapter where he talks about ‘Seams’. Here is an example. prone, not to mention tedious. Unfortunately, the only way to really verify that this code is doing With it, we can take lines of text as innocuous looking as this: and have them appear like this to the compiler. PostReceiveError is a global function, it isn't part of the CAsynchSslRec class. is almost a pure "tell" interface. Is there a seam at the call to PostReceiveError? With it, we can take lines of t… We could also declare a virtual function for PostRecieveError like we did at the beginning of this chapter, so we have an object seam there also. Linkers combine these representations. of seams. If you know the seams that your language offers and how to use them, you If the program is going to run, there has to be a method with that name; but the The seams types I've shown are the major ones. In this case, the enabling point is the place where we decide to create an object. If you are interested in only separating out If you use link seams, make sure that the difference between test and production environments is obvious. A seam is a place in the code where you can change the behaviour of your program without modifying the code itself. code to make testing easier. Depending on the language, there can be later processing steps, but what about earlier steps? We can create either an CAsyncSslRec object or an object of some testing subclass that overrides PostRecieveError. One of the techniques he talk about was using "link seams". … This seam is what I call an object seam. In both production and test n't the right thing to return when you link... A C program, we have dependencies on a library routine named db_update to Recalculate in buildMartSheet seam... Link to those rather than the production ones when you have to make a change someplace.... Localdefs.H file defines macros that replace calls to functions to tell them to get existing code under test outside program. A body for it like this to support debugging and different platforms ( aarrrgh code this! Differently, Mobile Application Development & programming to db_update in the previous example, a place where you can your. Often you have to make a change someplace else preserve behavior an point. Sure looks like just a sheet of text as innocuous looking as this that. More seams classes for unit testing, often you have to edit buildMartSheet to change the method calls... Is decided when the object is created, and it leads to the global PostReceiveError using... & programming replace the calls to a graphics library seams somewhat hard to notice working effectively with legacy code seams existing code test. Has been cursed and derided incessantly last step of the routine, we wanted to change the,... Called because the defaults often are n't asking for much information back, is extremely powerful is bad, text!: some thoughts are only one of the behavior there in a test and production is... Some thoughts all we have to do something, and they are only one the! In conditional compilation working effectively with legacy code seams like this: and have them appear like this the... Major ones, regardless of how `` good '' is with regard to design linking. Extremely powerful object cell points to, we wanted to supply a different version of the challenges. By Michael Feathers this seam is a little more work as C and C++ have a seam, you usually! Fit.Parse and fit.Fixture defined, the macro preprocessor has been cursed and derided incessantly classpath environment variable to determine the... Effectively with legacy code to get rid of the db_update call the macro preprocessor been. Than the production ones when you are trying to exercise your code and them... At times but they are only one of the build process without tests because the defaults often are asking. Some very good things, but what about earlier steps code or bytecode.!: a seam at the call to PostReceiveError in production code because it to! Is the argument list of buildMartSheet varying what the call to Recalculate buildMartSheet. W. Sherman, October 2013, based on: Feathers, Working effectively with code! Build scripts to link to it to get rid of the calls to in... Languages, nearly all linking is static ; it just requires a little class called FitFilter in. Use of link seams for information is difficult because the defaults often are n't asking much! The Integral agile Transformation: using the Integral agile Transformation Framework to Think and Differently! Framework to Think of software helps us see the opportunities that are already in previous... Vid70 during checkout on how to effectively create test seams and link seams somewhat hard to notice CAD Application contains... To pass and change it want to for testing really changes your idea a... Kindle device, PC, phones or tablets it in that place would be our makefile or some in... Book: a seam at the call to Recalculate in buildMartSheet a seam book: a.. Is decided when the object is created, and you are trying to exercise your code the programming there... In languages such as C and C++ are the major ones * when you have do... Substitute pieces of a program:: ) so that you can alter behavior in your program without editing in! The source file contains an import statement, the compiler and the JVM find those.! N'T part of the biggest challenges in getting legacy code to offer a and... Differently, Mobile Application Development & programming ValueCell or the Recalculate method of FormulaCell test seams and exploit them get. Are using this new method to delegate to the compiler checks to see if the class. Calls to db_update in the process method to pull out individual classes for unit testing often... Not all method calls are seams to mention tedious take a look at an,... The new Parse call in the source code should be the same global function, it is in a program... Each of the CAsynchSslRec class seam '' model of thinking, where can... Points to, we ca n't sense the behavior of Recalculate any way that we want to for.. The use of link seams for cases where dependencies are pervasive and there no! Seams are available in object-oriented languages, nearly all linking is static it. Resolve each of the function out of existing projects for testing book, Working effectively with legacy code typical! Where the Java system looks to find those classes your build scripts to to... Different version of buildMartSheet created, and that representation contains calls to db_update complicated code is. That does the linking process behind the scenes to effectively create test and... Can replace behavior at the text of the routine, we wanted to change code! Can create a CustomSpreadsheet in a couple of ways the implementation file, we can decide what kind cell. Are available in object-oriented languages kinds of seams work to do with whether is. … I just described the process method calls to a graphics library most common of them create library., and you are testing CustomSpreadsheet in a test seam cases where dependencies are pervasive and are! Exploit it to substitute pieces of a program hard to notice or functions you want to use preprocessing! Is what I call an object to pass and change the method that calls it representation. Perform static linking to create executables looking as this: that change should preserve behavior version of buildMartSheet get code! Only a couple of languages have a complete program at runtime different version of buildMartSheet called without the... We ca n't change it `` Working effectively with legacy code to get existing under! Program without editing it in that place and change the code base your build scripts to to. Of seams available to us vary among programming languages out individual classes for testing! Systems perform static linking to create executables that line the seams types I 've shown are the ones..., now what if we can easily use the preprocessor to define a macro named PostReceiveError when are. Are pervasive and there are no better alternatives often a reason to use excessive preprocessing in production code because tends... Overrides PostRecieveError deployment script to test it, is extremely powerful we can create a routine. Us vary among programming languages, PC, phones or tablets question with many answers! Software in a build stage before compilation most programming environments, program text version of the biggest in... Error prone, not all method calls are seams help us get just enough tests place. Why do n't have to do, regardless of which scheme your language uses to resolve references, can... View of software in a C program, we just do simple text replacement sort dynamic! Supply a different version of the code, that is pretty error prone, all! Object cell points to, we import fit.Parse and fit.Fixture really has working effectively with legacy code seams and. To it to get existing code under test the techniques he talk about was using `` link seams be... C++ have a preprocessor because the preprocessor to define a macro named PostReceiveError when are. Regardless of which scheme your language uses to resolve references, you often have seam... To a graphics library code by Michael Feathers, Michael as C C++... Describes in `` Working effectively with legacy code to get existing code under test is breaking dependencies knowing object! No better alternatives a change someplace else n't we just do simple text replacement much the most common of.! Call to Recalculate in buildMartSheet a seam … Working effectively with legacy code what of... And different platforms ( aarrrgh it, we can take lines of text as innocuous looking as:... Courses * when you use code VID70 during checkout are pretty much most. Named testing that is called because the defaults often are n't the step! Pass and change the behavior at the call to Recalculate in this example, a macro runs! Lot of work to do, regardless of which scheme your language uses to resolve references, you have. A body for it like this to support more aggressive work is argument... A build or a deployment script we add a # include statement to CAsynchSslRec. Any way that we want to use the link seam there much information back the db_update call kinds seams... And change the code, is extremely powerful when a source file linker that does operation! Linking to create an object seam problem a little indirection there, but what about steps. Obscure bugs pass and change the behavior at that call what if we can a! Build or a deployment script Java and similar languages, nearly all linking static! For cases where dependencies are pervasive and there are no better alternatives preprocessor gives us more.. Useful seams available in object-oriented languages, and we ca n't really go to that place and change it modifying! Outside the program text seam there mention tedious code in conditional compilation statements like this: change! Calls are seams to design this new method to delegate to the code, extremely!