Test
Driven
Development
Debugging
  Sucks

            Testing
            Rocks
Bugfixing
Cost




                      Bugs




•      Cost of bugfix = Number of bugs x Cost per fix, but...

•      How ...
Bugfixing
          Tests
Cost




                      Bugs/Features




•      Cost of tests = Number and complexity of...
Test
Automation
 Lifecycle
Fixture

all the things we need to
  have in place in order
 to run a test and expect
   a particular outcome
Fixture Setup
                 Fixture


    Steps

Fixture Setup
SUT


 System Under Test
is whatever thing we
     are testing
Exercise SUT
                      Fixture


    Steps
                SUT
Fixture Setup

Exercise SUT
Verify Result
                       Fixture


    Steps
                 SUT
Fixture Setup

Exercise SUT

Verify Result
“Don't call us, we'll call you”
Fixture Teardown
                         Fixture


     Steps
                   SUT
 Fixture Setup

 Exercise SUT

  Ver...
a test is a good one if...
• Is really automatic
 • Should be easy to invoke one or more tests
 • Must determine for itsel...
the kind of test is not
determined by the used tool
Unit tests
A test is not a unit test if:
   1. It talks to a database
   2. It communicates across the network
   3. It to...
public void marriageIsSimmetric() {
    Customer alice = new Customer("alice");
    Customer bob = new Customer("bob");

 ...
public void marriageIsSimmetric() {
    Customer alice = new Customer("alice");
    Customer bob = new Customer("bob");

 ...
public void marriageIsSimmetric() {
    Customer alice = new Customer("alice");
    Customer bob = new Customer("bob");

 ...
public void marriageIsSimmetric() {
    Customer alice = new Customer("alice");
    Customer bob = new Customer("bob");

 ...
Test-Driven
Development
As a developer,
I want to learn TDD,
  so that I can write
clean code that works
Clean code that works
  Clean code is simple and direct. Clean code
 reads like well-written prose. Clean code never
obscu...
Clean code that works
 Clean code always looks like it was written by
  someone who cares. There is nothing obvious
 that ...
Clean code that works

You know you are working on clean code when
  each routine you read turns out to be pretty
much wha...
Simple design

The code is simple enough when it:
  0. Pass all the tests
  1. Expresses every idea that we need to expres...
Clean code that works


• First we'll solve the “that works” part
• Then we'll solve the “clean code” part
Code that works could Smell




         Refactoring by Martin Fowler
... then Refactor

 Is the process of changing a software
system in such a way that it does not
   alter the external beha...
through small steps




          Refactoring by Martin Fowler
... fight the Smells
  Smell                  Common Refactorings
Duplicated Code   Extract Method, Extract Class, Pull-Up ...
... fight the Smells
    Smell                  Common Refactorings
 Shotgun Surgery                 Move Method, Move Fiel...
an example of
Refactoring and
   Unit tests
public class VobasBackupService implements Runnable {

    public void run() {
        Map fileDetails = new Hashtable();
...
WTF?!?
import java.util.*;

public class FileDetail {




                                                                   make...
is supposed
to work, but
how it works?
prepare your engine :-)
import org.junit.* ;                   import org.junit.* ;
import static org.junit.Assert.* ;    ...
Untestable
public void run() {
    try {
        Map fileDetails = new Hashtable();
        BufferedReader reader = new Bu...
Extract Method
public void run() {
    try {
        dontKnowWhatItDoes(MainFrame.WATCHED_DATA);

    } catch (FileNotFoun...
doing refactoring
  without tests
    is unsafe
Characterization Test
public class VobasBackupServiceCharacterizationTest {

    private List<File> directoriesToCleanup;
...
Characterization Test
@Test public void backupOneDirectoryWithTwoFreshFiles() throws Exception {
    VobasBackupService se...
Magic Number
@Test public void backupOneDirectoryWithTwoFreshFiles() throws Exception {
    VobasBackupService service = n...
Syntax Noise
     private void deleteDirectory(File directoryToDelete) throws Exception {
         if (directoryToDelete.i...
Syntax Noise
     private void deleteDirectory(File directoryToDelete) throws Exception {
         if (directoryToDelete.i...
now we can play safe
// read all directories to backup from a file
BufferedReader reader = new BufferedReader(new FileRead...
now we can play safe
// select only files to backup in directory
File[] files = new File(directoryName).listFiles(new File...
now we can play safe
   // save all details on files to .vobas file
   ObjectOutput objectOutput = new ObjectOutputStream(...
narrow your target
        and your tests
// for each of those directory
String directoryName = reader.readLine();
while (...
Extract Method
// for each of those directory
String directoryName = reader.readLine();
while (directoryName != null) {

 ...
Extract Method

public Map readDetailsOnFilesFrom(String directoryPath) throws ... {
    Map fileDetails = new Hashtable()...
Extract Method


// for each of those directory
String directoryName = reader.readLine();
while (directoryName != null) {
...
Extract Method


// for each of those directory
String directoryName = reader.readLine();
while (directoryName != null) {
...
Duplicated Code, Complex Conditional
// if no previous details are given
if (fileDetail == null) {
    // send to backup
 ...
Consolidate duplicated conditional fragments
// if no previous details are given
if (fileDetail == null) {
    // send to ...
Consolidate duplicated conditional fragments
// if no previous details are given
if (fileDetail == null) {

     // send t...
Consolidate duplicated conditional fragments
// if no previous details are given or
// if details are given but file has b...
Extract Method
for (File file : files) {
    FileDetail fileDetail = (FileDetail) fileDetails.get(file.getName());

    if...
Extract Method

for (File file : files) {
    FileDetail fileDetail = (FileDetail) fileDetails.get(file.getName());

    i...
Rename Method

public void dontKnowWhatItDoes(String directoryPathToBackup) throws ... {
     ...
}




public void backup...
Extract Method

public void backupDirectories(String listOfDirectoriesToBackup) throws ... {
    ...
    for (File file : ...
Extract Method
public void backupDirectories(String listOfDirectoriesToBackup) throws ... {
    BufferedReader reader = ne...
Replace temporary variable with Query


public void backupDirectory(String directoryPath) throws ... {
    Map fileDetails...
Replace temporary variable with Query


public void backupDirectory(String directoryPath) throws ... {
    Map fileDetails...
Introduce Generics


public void backupDirectory(String directoryPath) throws ... {
    Map fileDetails = readDetailsOnFil...
Introduce Generics



public void backupDirectory(String directoryPath) throws ... {
    Map<String, FileDetail> fileDetai...
Inconsistent Name
public void backupDirectories(String listOfDirectoriesToBackup) throws ... {
    BufferedReader reader =...
Extract Method, replace For with Loop
public void run() {
    try {
        backupDirectories(listOfDirectoriesToBackup(Ma...
public void run() {
    try {
        backupDirectories(listOfDirectoriesToBackup(MainFrame.WATCHED_DATA));

    } catch (...
Feature Envy, Large Class
public void writeDetailsOnFilesTo(String directoryPath, Map<String, FileDetail> fileDetails) thr...
Primitive Obsession, Data Clumps
public void writeDetailsOnFilesTo(String directoryPath, Map<String, FileDetail> fileDetai...
Extract Class
class BackupReport {

    public Map<String, FileDetail> fileDetails;

    private BackupReport(File directo...
Extract Class



public void backupDirectory(String directoryPath) throws ... {
    BackupReport lastBackupReport = Backup...
Feature Envy



public void backupDirectory(String directoryPath) throws ... {
    BackupReport lastBackupReport = BackupR...
Move Method, Rename Method



public void backupDirectory(String directoryPath) throws ... {
    BackupReport lastBackupRe...
Inconsistent Name



public void backupDirectory(String directoryPath) throws ... {
    BackupReport lastBackupReport = Ba...
Rename Class, Replace Data Value with Object



public void backupDirectory(File directoryToBackup) throws ... {
    Direc...
public void run() {
    try {
        backupDirectories(listOfDirectoriesToBackup(MainFrame.WATCHED_DATA));
    } catch (E...
class BackupPlan {

    public BackupPlan(File configuration) throws BackupFailedException {
        this.directoriesToBac...
class DirectoryBackupService {

    public DirectoryBackupService(File directoryToBackup) throws BackupFailedException {
 ...
Test-Driven
Development
   Cycle
Write a test
public class AdderTest {
  @Test
  public void testTwoPlusThree() {
    Adder a = new Adder();
    assertEqua...
Now it compiles
public class AdderTest {
  @Test
  public void testTwoPlusThree() {
    Adder a = new Adder();
    assertE...
Red bar!
public class AdderTest {
  @Test
  public void testTwoPlusThree() {
    Adder a = new Adder();
    assertEquals(5...
Just pretend
public class AdderTest {
  @Test
  public void testTwoPlusThree() {
    Adder a = new Adder();
    assertEqua...
Remove the duplicated “5”
   public class AdderTest {
     @Test
     public void testTwoPlusThree() {
       Adder a = ne...
The procedure

1. Write a test

2. Make it compile
                  Expected 5, was 0

3. Make it pass

4. Refactor
Red

Refactor             Green




   Repeat every 2-10 min.
It’s not about testing

• TDD is a design technique
• The tests are not the main point
• The design emerges in small steps
Clean code, why?
Clean code, why?

• Design is the great accelerator:
• If you drop quality for speed, you will get neither
• If you aim fo...
Test first, why?

• You think code from the point of view of the
  caller
• This perspective makes for better design
• Test...
Refactor, why?
Refactor, why?
• What is clean code today could be bad code
  tomorrow
• Refactoring is when I do design
• Design emerges,...
No silver bullet

• Needs lots of practice
• Requires discipline
• Must think and be alert at all times!
Refactoring In Tdd The Missing Part
Refactoring In Tdd The Missing Part
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Refactoring In Tdd The Missing Part

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Refactoring In Tdd The Missing Part

  1. Test Driven Development
  2. Debugging Sucks Testing Rocks
  3. Bugfixing Cost Bugs • Cost of bugfix = Number of bugs x Cost per fix, but... • How many bugs do you plan to have? • How hard do you think they are to fix?
  4. Bugfixing Tests Cost Bugs/Features • Cost of tests = Number and complexity of features • How many features do you plan to have? • How complex they are?
  5. Test Automation Lifecycle
  6. Fixture all the things we need to have in place in order to run a test and expect a particular outcome
  7. Fixture Setup Fixture Steps Fixture Setup
  8. SUT System Under Test is whatever thing we are testing
  9. Exercise SUT Fixture Steps SUT Fixture Setup Exercise SUT
  10. Verify Result Fixture Steps SUT Fixture Setup Exercise SUT Verify Result
  11. “Don't call us, we'll call you”
  12. Fixture Teardown Fixture Steps SUT Fixture Setup Exercise SUT Verify Result Fixture Teardown
  13. a test is a good one if... • Is really automatic • Should be easy to invoke one or more tests • Must determine for itself whether it passed or failed • Test everything that’s likely to break • Must be independent from the environment and each other test • Should be repeatable, could be run over and over again, in any order and produce the same results • The code is clean as the production code
  14. the kind of test is not determined by the used tool
  15. Unit tests A test is not a unit test if: 1. It talks to a database 2. It communicates across the network 3. It touches the file system 4. You have to do things to your environment to run it (eg, change config files) Tests that do this are integration tests Michael Feathers
  16. public void marriageIsSimmetric() { Customer alice = new Customer("alice"); Customer bob = new Customer("bob"); bob.marry(alice); assertTrue(bob.isMarriedTo(alice)); assertTrue(alice.isMarriedTo(bob)); } Simple Unit Test
  17. public void marriageIsSimmetric() { Customer alice = new Customer("alice"); Customer bob = new Customer("bob"); bob.marry(alice); assertTrue(bob.isMarriedTo(alice)); assertTrue(alice.isMarriedTo(bob)); } Fixture Setup
  18. public void marriageIsSimmetric() { Customer alice = new Customer("alice"); Customer bob = new Customer("bob"); bob.marry(alice); assertTrue(bob.isMarriedTo(alice)); assertTrue(alice.isMarriedTo(bob)); } Exercise SUT
  19. public void marriageIsSimmetric() { Customer alice = new Customer("alice"); Customer bob = new Customer("bob"); bob.marry(alice); assertTrue(bob.isMarriedTo(alice)); assertTrue(alice.isMarriedTo(bob)); } Verify Result
  20. Test-Driven Development
  21. As a developer, I want to learn TDD, so that I can write clean code that works
  22. Clean code that works Clean code is simple and direct. Clean code reads like well-written prose. Clean code never obscures the designer’s intent but rather is full of crisp abstractions and straightforward lines of control Grady Booch
  23. Clean code that works Clean code always looks like it was written by someone who cares. There is nothing obvious that you can do to make it better. All of those things were thought about by the code’s author, and if you try to imagine improvements, you’re led back to where you are, sitting in appreciation of the code someone left for you, code left by someone who cares deeply about the craft. Michael Feathers
  24. Clean code that works You know you are working on clean code when each routine you read turns out to be pretty much what you expected.You can call it beautiful code when the code also makes it look like the language was made for the problem Ward Cunningham
  25. Simple design The code is simple enough when it: 0. Pass all the tests 1. Expresses every idea that we need to express 2. Contains no duplication 3. Has the minimum number of classes and functions (In this order) Adapted from Extreme Programming Installed by Ron Jeffries et al.
  26. Clean code that works • First we'll solve the “that works” part • Then we'll solve the “clean code” part
  27. Code that works could Smell Refactoring by Martin Fowler
  28. ... then Refactor Is the process of changing a software system in such a way that it does not alter the external behaviour of the code yet improves its internal structure Martin Fowler
  29. through small steps Refactoring by Martin Fowler
  30. ... fight the Smells Smell Common Refactorings Duplicated Code Extract Method, Extract Class, Pull-Up Method, Template Method Feature Envy Move Method, Move Field, Extract Method Extract Class, Extract Subclass, Extract Interface, Replace Data Large Class Value with Object Extract Method, Replace Temporary Variable with Query, Replace Long Method Method with Method Object, Decompose Conditional
  31. ... fight the Smells Smell Common Refactorings Shotgun Surgery Move Method, Move Field, Inline Class Replace Parameter with Method, Introduct Parameter Object, Long Parameter List Preserve Whole Object Data Class Move Method, Encapsulate Field, Encapsulate Collection Comments Extract Method, Introduce Assertion
  32. an example of Refactoring and Unit tests
  33. public class VobasBackupService implements Runnable { public void run() { Map fileDetails = new Hashtable(); try { BufferedReader reader = new BufferedReader(new FileReader(MainFrame.WATCHED_DATA)); String directoryName = reader.readLine(); File fileData = new File(directoryName, ".vobas"); while (directoryName != null) { if (!fileData.exists()) { fileData.createNewFile(); } else { ObjectInputStream fileDetailsReader = new ObjectInputStream(new FileInputStream(fileData)); FileDetail fileDetail = (FileDetail) fileDetailsReader.readObject(); while (fileDetail != null) { fileDetails.put(fileDetail.getName(), fileDetail); try { fileDetail = (FileDetail) fileDetailsReader.readObject(); } catch (EOFException e) { break; } } } File[] files = new File(directoryName).listFiles(); for (File file : files) { FileDetail fileDetail = (FileDetail) fileDetails.get(file.getName()); if (fileDetail == null) { ScpTo.send(directoryName + File.separatorChar + file.getName()); fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); } else if (file.lastModified() > fileDetail.getModificationDate().getTime()) { ScpTo.send(directoryName + File.separatorChar + file.getName()); fileDetails.remove(file.getName()); fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); } } ObjectOutput objectOutput = new ObjectOutputStream(new FileOutputStream(new File(directoryName, ".vobas"))); for (FileDetail fileDetail : fileDetails.values()) { objectOutput.writeObject(fileDetail); } objectOutput.close(); directoryName = reader.readLine(); } reader.close(); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (IOException e) {
  34. WTF?!?
  35. import java.util.*; public class FileDetail { make it private Date lastModified; private String fileName; public FileDetail(Date lastModified, String fileName) { this.lastModified = lastModified; compile this.fileName = fileName; } public Date getModificationDate() { return this.lastModified; } public String getName() { return this.fileName; } } public class MainFrame { } public static final String WATCHED_DATA = "/dev/null"; stub public class ScpTo { public static void send(String filePathToSend) { } // TODO: no need to implement :-( dependencies }
  36. is supposed to work, but how it works?
  37. prepare your engine :-) import org.junit.* ; import org.junit.* ; import static org.junit.Assert.* ; import static org.junit.Assert.* ; public class StubTest { public class StubTest { @Test @Test public void shouldAlwaysWork() { public void shouldNeverWork() { assertTrue(true); assertTrue(false); } } } }
  38. Untestable public void run() { try { Map fileDetails = new Hashtable(); BufferedReader reader = new BufferedReader(new FileReader(MainFrame.WATCHED_DATA)); ... } catch (FileNotFoundException e) { ... } }
  39. Extract Method public void run() { try { dontKnowWhatItDoes(MainFrame.WATCHED_DATA); } catch (FileNotFoundException e) { ... } public void dontKnowWhatItDoes(String directoryPathToBackup) throws ... { BufferedReader reader = new BufferedReader(new FileReader(directoryPathToBackup)); Map fileDetails = new Hashtable(); String directoryName = reader.readLine(); File fileData = new File(directoryName, ".vobas"); while (directoryName != null) { ... } reader.close(); }
  40. doing refactoring without tests is unsafe
  41. Characterization Test public class VobasBackupServiceCharacterizationTest { private List<File> directoriesToCleanup; @Before public void setUp() throws Exception { directoriesToCleanup = new ArrayList<File>(); } @After public void tearDown() throws Exception { for (File directoryToCleanup : directoriesToCleanup) { deleteDirectory(directoryToCleanup); } ScpTo.sended = new ArrayList<String>(); } @Test public void backupOneDirectoryWithOneFreshFile() throws Exception { VobasBackupService service = new VobasBackupService(); File oneDirectoryWithOneFile = createDirectoryToBackupWithFiles(1); File listOfDirectoriesToBackup = listOfDirectoriesToBackupIntoFile(oneDirectoryWithOneFile); service.backup(listOfDirectoriesToBackup.getAbsolutePath()); assertEquals(1, ScpTo.sended.size()); directoriesToCleanup.add(oneDirectoryWithOneFile); }
  42. Characterization Test @Test public void backupOneDirectoryWithTwoFreshFiles() throws Exception { VobasBackupService service = new VobasBackupService(); File oneDirectoryWithTwoFiles = createDirectoryToBackupWithFiles(2); File listOfDirectoriesToBackup = listOfDirectoriesToBackupIntoFile(oneDirectoryWithTwoFiles); service.backup(listOfDirectoriesToBackup.getAbsolutePath()); assertEquals(2, ScpTo.sended.size()); directoriesToCleanup.add(oneDirectoryWithTwoFiles); } @Test public void backupTwoDirectoriesWithOneFreshFile() throws Exception { VobasBackupService service = new VobasBackupService(); File oneDirectoryWithOneFile = createDirectoryToBackupWithFiles(1); File anotherDirectoryWithOneFile = createDirectoryToBackupWithFiles(1); File listOfDirectoriesToBackup = listOfDirectoriesToBackupIntoFile( oneDirectoryWithOneFile, anotherDirectoryWithOneFile); service.backup(listOfDirectoriesToBackup.getAbsolutePath()); assertEquals(2, ScpTo.sended.size()); directoriesToCleanup.add(oneDirectoryWithOneFile); directoriesToCleanup.add(anotherDirectoryWithOneFile); }
  43. Magic Number @Test public void backupOneDirectoryWithTwoFreshFiles() throws Exception { VobasBackupService service = new VobasBackupService(); File oneDirectoryWithTwoFiles = createDirectoryToBackupWithFiles(2); File listOfDirectoriesToBackup = listOfDirectoriesToBackupIntoFile(oneDirectoryWithTwoFiles); service.backup(listOfDirectoriesToBackup.getAbsolutePath()); assertEquals(2, ScpTo.sended.size()); directoriesToCleanup.add(oneDirectoryWithTwoFiles); } replace Magic Number with Expression @Test public void backupOneDirectoryWithTwoFreshFiles() throws Exception { VobasBackupService service = new VobasBackupService(); File oneDirectoryWithTwoFiles = createDirectoryToBackupWithFiles(2); File listOfDirectoriesToBackup = listOfDirectoriesToBackupIntoFile(oneDirectoryWithTwoFiles); service.backup(listOfDirectoriesToBackup.getAbsolutePath()); assertEquals(oneDirectoryWithTwoFiles.list().length, ScpTo.sended.size()); directoriesToCleanup.add(oneDirectoryWithTwoFiles); }
  44. Syntax Noise private void deleteDirectory(File directoryToDelete) throws Exception { if (directoryToDelete.isDirectory()) { String[] children = directoryToDelete.list(); for (int i=0; i<children.length; i++) { deleteDirectory(new File(directoryToDelete, children[i])); } } if (!directoryToDelete.delete()) { throw new Exception("unable to delete " + directoryToDelete.getAbsolutePath()); } } replace For with Loop private void deleteDirectory(File directoryToDelete) throws Exception { if (directoryToDelete.isDirectory()) { for (File child : directoryToDelete.listFiles()) { deleteDirectory(child); } } assert directoryToDelete.delete() : "unable to delete " + directoryToDelete.getAbsolutePath()); }
  45. Syntax Noise private void deleteDirectory(File directoryToDelete) throws Exception { if (directoryToDelete.isDirectory()) { String[] children = directoryToDelete.list(); for (int i=0; i<children.length; i++) { deleteDirectory(new File(directoryToDelete, children[i])); } } if (!directoryToDelete.delete()) { throw new Exception("unable to delete " + directoryToDelete.getAbsolutePath()); } } replace Test with Assertion private void deleteDirectory(File directoryToDelete) throws Exception { if (directoryToDelete.isDirectory()) { for (File child : directoryToDelete.listFiles()) { deleteDirectory(child); } } assert directoryToDelete.delete() : "unable to delete " + directoryToDelete.getAbsolutePath()); }
  46. now we can play safe // read all directories to backup from a file BufferedReader reader = new BufferedReader(new FileReader(directoryPathToBackup)); // for each of those directory String directoryName = reader.readLine(); while (directoryName != null) { // get details on files in these directory Map fileDetails = new Hashtable(); File fileData = new File(directoryName, ".vobas"); if (!fileData.exists()) { fileData.createNewFile(); } else { ObjectInputStream fileDetailsReader = new ObjectInputStream( new FileInputStream(fileData)); FileDetail fileDetail = (FileDetail) fileDetailsReader.readObject(); while (fileDetail != null) { fileDetails.put(fileDetail.getName(), fileDetail); try { fileDetail = (FileDetail) fileDetailsReader.readObject(); } catch (EOFException e) { break; } } }
  47. now we can play safe // select only files to backup in directory File[] files = new File(directoryName).listFiles(new FilenameFilter() { public boolean accept(File directory, String fileName) { return ! fileName.equals(".vobas"); } }); // for each of those files for (File file : files) { FileDetail fileDetail = (FileDetail) fileDetails.get(file.getName()); // if no previous details are given if (fileDetail == null) { // send to backup ScpTo.send(directoryName + File.separatorChar + file.getName()); // save details fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); // if details are given but file has been modified } else if (file.lastModified() > fileDetail.getModificationDate().getTime()) { // send to backup ScpTo.send(directoryName + File.separatorChar + file.getName()); // save details fileDetails.remove(file.getName()); fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); } }
  48. now we can play safe // save all details on files to .vobas file ObjectOutput objectOutput = new ObjectOutputStream( new FileOutputStream(new File(directoryName, ".vobas"))); for (Object value : fileDetails.values()) { FileDetail fileDetail = (FileDetail) value; objectOutput.writeObject(fileDetail); } objectOutput.close(); // next directory to backup please... directoryName = reader.readLine(); } reader.close();
  49. narrow your target and your tests // for each of those directory String directoryName = reader.readLine(); while (directoryName != null) { Comment // read details on files in directory Map fileDetails = new Hashtable(); File fileData = new File(directoryName, ".vobas"); if (!fileData.exists()) { fileData.createNewFile(); } else { ObjectInputStream fileDetailsReader = new ObjectInputStream( new FileInputStream(fileData)); FileDetail fileDetail = (FileDetail) fileDetailsReader.readObject(); while (fileDetail != null) { fileDetails.put(fileDetail.getName(), fileDetail); try { fileDetail = (FileDetail) fileDetailsReader.readObject(); } catch (EOFException e) { break; } } }
  50. Extract Method // for each of those directory String directoryName = reader.readLine(); while (directoryName != null) { // read details on files in directory Map fileDetails = new Hashtable(); File fileData = new File(directoryName, ".vobas"); if (!fileData.exists()) { fileData.createNewFile(); } else { ObjectInputStream fileDetailsReader = new ObjectInputStream( new FileInputStream(fileData)); FileDetail fileDetail = (FileDetail) fileDetailsReader.readObject(); while (fileDetail != null) { fileDetails.put(fileDetail.getName(), fileDetail); try { fileDetail = (FileDetail) fileDetailsReader.readObject(); } catch (EOFException e) { break; } } }
  51. Extract Method public Map readDetailsOnFilesFrom(String directoryPath) throws ... { Map fileDetails = new Hashtable(); File fileData = new File(directoryPath, ".vobas"); if (!fileData.exists()) { fileData.createNewFile(); } else { ObjectInputStream fileDetailsReader = new ObjectInputStream( new FileInputStream(fileData)); FileDetail fileDetail = (FileDetail) fileDetailsReader.readObject(); while (fileDetail != null) { fileDetails.put(fileDetail.getName(), fileDetail); try { fileDetail = (FileDetail) fileDetailsReader.readObject(); } catch (EOFException e) { break; } } } return fileDetails; }
  52. Extract Method // for each of those directory String directoryName = reader.readLine(); while (directoryName != null) { // read details on files in directory Map fileDetails = readDetailsOnFilesFrom(directoryName); // select only files to backup in directory File[] files = new File(directoryName).listFiles(new FilenameFilter() { public boolean accept(File directory, String fileName) { return ! fileName.equals(".vobas"); } }); ...
  53. Extract Method // for each of those directory String directoryName = reader.readLine(); while (directoryName != null) { Map fileDetails = readDetailsOnFilesFrom(directoryName); // select only files to backup in directory File[] files = new File(directoryName).listFiles(new FilenameFilter() { public boolean accept(File directory, String fileName) { return ! fileName.equals(".vobas"); } }); ...
  54. Duplicated Code, Complex Conditional // if no previous details are given if (fileDetail == null) { // send to backup ScpTo.send(directoryName + File.separatorChar + file.getName()); // save details fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); // if details are given but file has been modified } else if (file.lastModified() > fileDetail.getModificationDate().getTime()) { // send to backup ScpTo.send(directoryName + File.separatorChar + file.getName()); // save details fileDetails.remove(file.getName()); fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); }
  55. Consolidate duplicated conditional fragments // if no previous details are given if (fileDetail == null) { // send to backup ScpTo.send(directoryName + File.separatorChar + file.getName()); // save details fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); // if details are given but file has been modified } else if (file.lastModified() > fileDetail.getModificationDate().getTime()) { // send to backup ScpTo.send(directoryName + File.separatorChar + file.getName()); // save details fileDetails.remove(file.getName()); fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); }
  56. Consolidate duplicated conditional fragments // if no previous details are given if (fileDetail == null) { // send to backup ScpTo.send(directoryName + File.separatorChar + file.getName()); // save details fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); // if details are given but file has been modified } else if (file.lastModified() > fileDetail.getModificationDate().getTime()) { // send to backup ScpTo.send(directoryName + File.separatorChar + file.getName()); // save details fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); }
  57. Consolidate duplicated conditional fragments // if no previous details are given or // if details are given but file has been modified if ((fileDetail == null) || (file.lastModified() > fileDetail.getModificationDate().getTime())) { // send to backup ScpTo.send(directoryName + File.separatorChar + file.getName()); // save details fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); }
  58. Extract Method for (File file : files) { FileDetail fileDetail = (FileDetail) fileDetails.get(file.getName()); if (noPrevioiusDetailsAreGiven(fileDetail) || fileHasBeenModifiedSinceLastBackup(fileDetail, file)) { // send to backup ScpTo.send(directoryName + File.separatorChar + file.getName()); // save details fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); } } private boolean noPrevioiusDetailsAreGiven(FileDetail fileDetail) { return fileDetail == null; } private boolean fileHasBeenModifiedSinceLastBackup(FileDetail fileDetail, File file) { return file.lastModified() > fileDetail.getModificationDate().getTime(); }
  59. Extract Method for (File file : files) { FileDetail fileDetail = (FileDetail) fileDetails.get(file.getName()); if (needBackup(fileDetail, file)) { // send to backup ScpTo.send(directoryName + File.separatorChar + file.getName()); // save details fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); } } private boolean needBackup(FileDetail fileDetail, File file) { return noPrevioiusDetailsAreGiven(fileDetail) || fileHasBeenModifiedSinceLastBackup(fileDetail, file); }
  60. Rename Method public void dontKnowWhatItDoes(String directoryPathToBackup) throws ... { ... } public void backupDirectories(String listOfDirectoriesToBackup) throws ... { for (File file : files) { FileDetail fileDetail = (FileDetail) fileDetails.get(file.getName()); if (needBackup(fileDetail, file)) { // send to backup ScpTo.send(directoryName + File.separatorChar + file.getName()); // save details fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); } }
  61. Extract Method public void backupDirectories(String listOfDirectoriesToBackup) throws ... { ... for (File file : files) { FileDetail fileDetail = (FileDetail) fileDetails.get(file.getName()); if (needBackup(fileDetail, file)) { backupFile(file); updateFileDetails(fileDetails, file); } } ... } private void backupFile(File fileToBackup) { ScpTo.send(file.getAbsolutePath()); } private void updateFileDetails(Map fileDetails, File file) { fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); }
  62. Extract Method public void backupDirectories(String listOfDirectoriesToBackup) throws ... { BufferedReader reader = new BufferedReader(new FileReader(listOfDirectoriesToBackup)); String directoryPath = reader.readLine(); while (directoryPath != null) { backupDirectory(directoryPath); directoryPath = reader.readLine(); } reader.close(); } public void backupDirectory(String directoryPath) throws ... { Map fileDetails = readDetailsOnFilesFrom(directoryPath); File[] files = filesToBackupInto(directoryPath); for (File file : files) { FileDetail fileDetail = (FileDetail) fileDetails.get(file.getName()); if (needBackup(fileDetail, file)) { backupFile(file); updateFileDetails(fileDetails, file); } } writeDetailsOnFilesTo(directoryPath, fileDetails); }
  63. Replace temporary variable with Query public void backupDirectory(String directoryPath) throws ... { Map fileDetails = readDetailsOnFilesFrom(directoryPath); File[] files = filesToBackupInto(directoryPath); for (File file : files) { FileDetail fileDetail = (FileDetail) fileDetails.get(file.getName()); if (needBackup(fileDetail, file)) { backupFile(file); updateFileDetails(fileDetails, file); } } writeDetailsOnFilesTo(directoryPath, fileDetails); }
  64. Replace temporary variable with Query public void backupDirectory(String directoryPath) throws ... { Map fileDetails = readDetailsOnFilesFrom(directoryPath); for (File file : filesToBackupInto(directoryPath)) { FileDetail fileDetail = (FileDetail) fileDetails.get(file.getName()); if (needBackup(fileDetail, file)) { backupFile(file); updateFileDetails(fileDetails, file); } } writeDetailsOnFilesTo(directoryPath, fileDetails); }
  65. Introduce Generics public void backupDirectory(String directoryPath) throws ... { Map fileDetails = readDetailsOnFilesFrom(directoryPath); for (File file : filesToBackupInto(directoryPath)) { FileDetail fileDetail = (FileDetail) fileDetails.get(file.getName()); if (needBackup(fileDetail, file)) { backupFile(file); updateFileDetails(fileDetails, file); } } writeDetailsOnFilesTo(directoryPath, fileDetails); }
  66. Introduce Generics public void backupDirectory(String directoryPath) throws ... { Map<String, FileDetail> fileDetails = readDetailsOnFilesFrom(directoryPath); for (File file : filesToBackupInto(directoryPath)) { if (needBackup(fileDetails, file)) { backupFile(file); updateFileDetails(fileDetails, file); } } writeDetailsOnFilesTo(directoryPath, fileDetails); }
  67. Inconsistent Name public void backupDirectories(String listOfDirectoriesToBackup) throws ... { BufferedReader reader = new BufferedReader(new FileReader(listOfDirectoriesToBackup)); String directoryPath = reader.readLine(); while (directoryPath != null) { backupDirectory(directoryPath); directoryPath = reader.readLine(); } reader.close(); }
  68. Extract Method, replace For with Loop public void run() { try { backupDirectories(listOfDirectoriesToBackup(MainFrame.WATCHED_DATA)); ... } } public List<File> listOfDirectoriesToBackup(String listOfDirectories) throws ... { List<File> directoriesToBackup = new ArrayList<File>(); BufferedReader reader = new BufferedReader(new FileReader(listOfDirectories)); String directoryName = reader.readLine(); while (directoryName != null) { directoriesToBackup.add(new File(directoryName)); directoryName = reader.readLine(); } return directoriesToBackup; } public void backupDirectories(List<File> listOfDirectoriesToBackup) throws ... { for (File directoryToBackup : listOfDirectoriesToBackup) { backupDirectory(directoryToBackup.getAbsolutePath()); } }
  69. public void run() { try { backupDirectories(listOfDirectoriesToBackup(MainFrame.WATCHED_DATA)); } catch (Exception e) { throw new RuntimeException(e); } } public void backupDirectories(List<File> listOfDirectoriesToBackup) throws ... { for (File directoryToBackup : listOfDirectoriesToBackup) { backupDirectory(directoryToBackup.getAbsolutePath()); } } public void backupDirectory(String directoryPath) throws ... { Map<String, FileDetail> fileDetails = readDetailsOnFilesFrom(directoryPath); for (File file : filesToBackupInto(directoryPath)) { if (needBackup(fileDetails, file)) { backupFile(file); updateFileDetails(fileDetails, file); } } writeDetailsOnFilesTo(directoryPath, fileDetails); }
  70. Feature Envy, Large Class public void writeDetailsOnFilesTo(String directoryPath, Map<String, FileDetail> fileDetails) throws ... { ... } public Map<String, FileDetail> readDetailsOnFilesFrom(String directoryPath) throws ... { ... } private boolean needBackup(Map<String, FileDetail> fileDetails, File file) { FileDetail fileDetail = fileDetails.get(file.getName()); return noPrevioiusDetailsAreGiven(fileDetail) || fileHasBeenModifiedSinceLastBackup(fileDetail, file); } private boolean noPrevioiusDetailsAreGiven(FileDetail fileDetail) { return fileDetail == null; } private boolean fileHasBeenModifiedSinceLastBackup(FileDetail fileDetail, File file) { return file.lastModified() > fileDetail.getModificationDate().getTime(); } private void updateFileDetails(Map<String, FileDetail> fileDetails, File file) { fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); }
  71. Primitive Obsession, Data Clumps public void writeDetailsOnFilesTo(String directoryPath, Map<String, FileDetail> fileDetails) throws ... { ... } public Map<String, FileDetail> readDetailsOnFilesFrom(String directoryPath) throws ... { ... } private boolean needBackup(Map<String, FileDetail> fileDetails, File file) { FileDetail fileDetail = fileDetails.get(file.getName()); return noPrevioiusDetailsAreGiven(fileDetail) || fileHasBeenModifiedSinceLastBackup(fileDetail, file); } private boolean noPrevioiusDetailsAreGiven(FileDetail fileDetail) { return fileDetail == null; } private boolean fileHasBeenModifiedSinceLastBackup(FileDetail fileDetail, File file) { return file.lastModified() > fileDetail.getModificationDate().getTime(); } private void updateFileDetails(Map<String, FileDetail> fileDetails, File file) { fileDetails.put(file.getName(), new FileDetail(new Date(), file.getName())); }
  72. Extract Class class BackupReport { public Map<String, FileDetail> fileDetails; private BackupReport(File directoryToBackup) throws ... { fileDetails = new Hashtable<String, FileDetail>(); File fileData = new File(directoryToBackup, ".vobas"); if (!fileData.exists()) { fileData.createNewFile(); } else { ObjectInputStream fileDetailsReader = new ObjectInputStream(new FileInputStream(fileData)); FileDetail fileDetail = (FileDetail) fileDetailsReader.readObject(); while (fileDetail != null) { fileDetails.put(fileDetail.getName(), fileDetail); try { fileDetail = (FileDetail) fileDetailsReader.readObject(); } catch (EOFException e) { break; } } } } public static BackupReport readFrom(File directoryToBackup) throws ... { return new BackupReport(directoryToBackup); } public static BackupReport readFrom(String pathToDirectoryToBackup) throws ... { return new BackupReport(new File(pathToDirectoryToBackup)); } }
  73. Extract Class public void backupDirectory(String directoryPath) throws ... { BackupReport lastBackupReport = BackupReport.readFrom(directoryPath); for (File file : filesToBackupInto(directoryPath)) { if (needBackup(lastBackupReport.fileDetails, file)) { backupFile(file); updateFileDetails(lastBackupReport.fileDetails, file); } } writeDetailsOnFilesTo(directoryPath, lastBackupReport.fileDetails); }
  74. Feature Envy public void backupDirectory(String directoryPath) throws ... { BackupReport lastBackupReport = BackupReport.readFrom(directoryPath); for (File file : filesToBackupInto(directoryPath)) { if (needBackup(lastBackupReport.fileDetails, file)) { backupFile(file); updateFileDetails(lastBackupReport.fileDetails, file); } } writeDetailsOnFilesTo(directoryPath, lastBackupReport.fileDetails); }
  75. Move Method, Rename Method public void backupDirectory(String directoryPath) throws ... { BackupReport lastBackupReport = BackupReport.readFrom(directoryPath); for (File file : filesToBackupInto(directoryPath)) { if (lastBackupReport.needBackup(file)) { backupFile(file); lastBackupReport.update(file); } } lastBackupReport.save(); }
  76. Inconsistent Name public void backupDirectory(String directoryPath) throws ... { BackupReport lastBackupReport = BackupReport.readFrom(directoryPath); for (File file : filesToBackupInto(directoryPath)) { if (lastBackupReport.needBackup(file)) { backupFile(file); lastBackupReport.update(file); } } lastBackupReport.save(); }
  77. Rename Class, Replace Data Value with Object public void backupDirectory(File directoryToBackup) throws ... { DirectoryBackupStatus directoryBackupStatus = new DirectoryBackupStatus(directoryToBackup); for (File file : filesToBackupInto(directoryToBackup)) { if (directoryBackupStatus.needBackup(file)) { backupFile(file); directoryBackupStatus.update(file); } } directoryBackupStatus.save(); }
  78. public void run() { try { backupDirectories(listOfDirectoriesToBackup(MainFrame.WATCHED_DATA)); } catch (Exception e) { throw new RuntimeException(e); } } public void backupDirectories(List<File> listOfDirectoriesToBackup) throws ... { for (File directoryToBackup : listOfDirectoriesToBackup) { backupDirectory(directoryToBackup); } } public void backupDirectory(File directoryToBackup) throws ... { DirectoryBackupStatus directoryBackupStatus = new DirectoryBackupStatus(directoryToBackup); for (File file : filesToBackupInto(directoryToBackup)) { if (directoryBackupStatus.needBackup(file)) { backupFile(file); directoryBackupStatus.update(file); } } directoryBackupStatus.save(); }
  79. class BackupPlan { public BackupPlan(File configuration) throws BackupFailedException { this.directoriesToBackup = directoriesToBackup(backupPlan); } public void runWith(BackupService backupService) throws BackupFailedException { for (File directoryToBackup : directoriesToBackup) { new DirectoryBackupService(directoryToBackup).backupWith(backupService); } } private List<File> directoriesToBackup(File configuration) throws BackupFailedException { ... } private List<File> directoriesToBackup; }
  80. class DirectoryBackupService { public DirectoryBackupService(File directoryToBackup) throws BackupFailedException { readBackupStatusFrom(directoryToBackup); } public void backupWith(BackupService backupService) throws BackupFailedException { for (File file : listOfFilesToBackup()) { if (needBackup(file)) { backupService.backup(file); update(file); } } save(); } ... }
  81. Test-Driven Development Cycle
  82. Write a test public class AdderTest { @Test public void testTwoPlusThree() { Adder a = new Adder(); assertEquals(5, a.add(2, 3)); } }
  83. Now it compiles public class AdderTest { @Test public void testTwoPlusThree() { Adder a = new Adder(); assertEquals(5, a.add(2, 3)); } } public class Adder { public int add(int a, int b) { return 0; } }
  84. Red bar! public class AdderTest { @Test public void testTwoPlusThree() { Adder a = new Adder(); assertEquals(5, a.add(2, 3)); } } public class Adder { public int add(int a, int b) { return 0; } } Expected 5, was 0
  85. Just pretend public class AdderTest { @Test public void testTwoPlusThree() { Adder a = new Adder(); assertEquals(5, a.add(2, 3)); } } public class Adder { public int add(int a, int b) { return 5; } }
  86. Remove the duplicated “5” public class AdderTest { @Test public void testTwoPlusThree() { Adder a = new Adder(); assertEquals(5, a.add(2, 3)); } } public class Adder { public int add(int a, int b) { return a+b; } }
  87. The procedure 1. Write a test 2. Make it compile Expected 5, was 0 3. Make it pass 4. Refactor
  88. Red Refactor Green Repeat every 2-10 min.
  89. It’s not about testing • TDD is a design technique • The tests are not the main point • The design emerges in small steps
  90. Clean code, why?
  91. Clean code, why? • Design is the great accelerator: • If you drop quality for speed, you will get neither • If you aim for quality... • ... and you know how to get it... • ... you will also be fast!
  92. Test first, why? • You think code from the point of view of the caller • This perspective makes for better design • Test coverage is a useful byproduct
  93. Refactor, why?
  94. Refactor, why? • What is clean code today could be bad code tomorrow • Refactoring is when I do design • Design emerges, with thought, care and small steps • I don’t claim I can guess the right design • Because I can: the tests support refactoring
  95. No silver bullet • Needs lots of practice • Requires discipline • Must think and be alert at all times!

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