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TestDrivenDevelopment
Debugging Sucks
Testing Rocks
Cos
t
Bugfixing
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?
Cos
t
Bugfixing
Bugs/Features
Tests
• Cost of tests = Number and complexity of features
• How many features do you plan to have?
• How complex they are?
TestAutomationLifecycle
all the things we need to have in place in order to run a test and expect
a particular outcome
Fixture
Fixture Setup
Steps
Fixture Setup
Fixture
System Under Testis whatever thing we
are testing
SUT
Exercise SUT
Steps
Exercise SUT
Fixture Setup
Fixture
SUT
Steps
Exercise SUT
Fixture Setup
Verify Result
Fixture
SUT
Verify Result
“Don't call us, we'll call you”
Steps
Exercise SUT
Fixture Teardown
Fixture Setup
Verify Result
Fixture
SUT
Fixture Teardown
• 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
a test is a good one if...
the kind of test is not determined by the used tool
Unit testsA 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
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
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
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
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
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
obscures the designer’s intent but rather is full of crisp abstractions and straightforward lines
of control
Grady Booch
Clean code that worksClean 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
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
Simple design
The code is simple enough when it:0. Pass all the tests1. Expresses every idea that we need to express2. Contains no duplication3. Has the minimum number of classes and functions
(In this order)
Adapted from Extreme Programming Installed by Ron Jeffries et al.
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
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
... then Refactor
Martin Fowler
Refactoring by Martin Fowler
through small steps
... 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
Large ClassExtract Class, Extract Subclass, Extract Interface, Replace Data
Value with Object
Long MethodExtract Method, Replace Temporary Variable with Query, Replace
Method with Method Object, Decompose Conditional
Smell Common Refactorings
Shotgun Surgery Move Method, Move Field, Inline Class
Long Parameter ListReplace Parameter with Method, Introduct Parameter Object,
Preserve Whole Object
Data Class Move Method, Encapsulate Field, Encapsulate Collection
Comments Extract Method, Introduce Assertion
... fight the Smells
an example ofRefactoring and
Unit tests
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) { // TODO Auto-generated catch block e.printStackTrace(); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); }
}
}
WTF?!?
import java.util.*;
public class FileDetail {
private Date lastModified; private String fileName;
public FileDetail(Date lastModified, String fileName) { this.lastModified = lastModified; 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"; }
public class ScpTo { public static void send(String filePathToSend) { // TODO: no need to implement :-( }
}
make itcompile
stubdependencies
is supposedto work, buthow it works?
import org.junit.* ;import static org.junit.Assert.* ;
public class StubTest { @Test public void shouldAlwaysWork() { assertTrue(true); }
}
import org.junit.* ;import static org.junit.Assert.* ;
public class StubTest { @Test public void shouldNeverWork() { assertTrue(false); }
}
prepare your engine :-)
public void run() { try { Map fileDetails = new Hashtable(); BufferedReader reader = new BufferedReader(new FileReader(MainFrame.WATCHED_DATA)); ...
} catch (FileNotFoundException e) { ... }}
Untestable
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(); }
Extract Method
doing refactoringwithout tests
is unsafe
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); }
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); }
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); }
Magic Number
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); }
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()); } }
Syntax Noise
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()); }
replace For with Loop
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()); } }
Syntax Noise
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()); }
replace Test with Assertion
// 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; } } }
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())); } }
now we can play safe
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();
narrow your targetand your tests
// 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; } } }
Comment
// 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; } } }
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; }
Extract Method
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"); } });
...
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"); } });
...
Duplicated Code, Complex Conditional
// if no previous details are givenif (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()));}
// if no previous details are givenif (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()));}
Consolidate duplicated conditional fragments
// if no previous details are givenif (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()));
}
Consolidate duplicated conditional fragments
// if no previous details are given or// if details are given but file has been modifiedif ((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()));
}
Consolidate duplicated conditional fragments
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();}
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); }
Extract Method
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())); }}
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)) { 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())); }
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); }
Extract Method
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); }
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); }
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); }
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); }
Introduce Generics
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(); }
Inconsistent Name
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()); } }
Extract Method, replace For with Loop
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); }
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())); }
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())); }
Primitive Obsession, Data Clumps
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)); }
}
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); }
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); }
Feature Envy
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(); }
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(); }
Inconsistent Name
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(); }
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(); }
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;
}
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(); }
... }
Test-Driven Development
Cycle
public class AdderTest { @Test
public void testTwoPlusThree() {Adder a = new Adder();assertEquals(5, a.add(2, 3));
}}
Write a test
Now it compilespublic 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; }}
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
Just pretendpublic 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; }}
Remove the duplicated “5”public class AdderTest {
@Testpublic 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; }}
1. Write a test
2. Make it compile
3. Make it pass
4. Refactor
The procedure
Expected 5, was 0
Red
GreenRefactor
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 for quality...
• ... and you know how to get it...
• ... you will also be fast!
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
Refactor, why?
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
No silver bullet
• Needs lots of practice
• Requires discipline
• Must think and be alert at all times!