EclipseCon Europe 2013: Take back Control over your Test Suite

We all know testing is important. Unfortunately, even the best intentions are often crushed by slow and brittle tests hindering development more than they actually help.

But this must not necessarily be the case. In this talk I want to present some simple techniques helping you to write better tests for your Eclipse plugins. In particular, the following topics will be covered:

- how to write maintainable tests that don't break on every change.
- how tests help you writing better code.
- how to speedup your test suite.
- how to avoid integration tests.

Transcript

1. TAKE BACK
   CONTROL OVER
   YOUR TEST
   SUITE
   SEBASTIAN BENZ
   E S R
   L A B S
   

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2. SLOW& BRITTLE
   …tests are no help
   

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3. #1 FOCUS YOUR TESTS
   

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4. Try it at home…
   

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5. Test your core functionality
   without Eclipse.
   Your Architecture
   thanks you!
   

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6. @Test public void generatesCode() {
   IProject project = workspace.getProject("MyProject");
   project.create(...);
   CodeGenerator codeGenerator = new CodeGenerator(project);
   !
   !
   !
   !
   }
   Input someInput = ...;
   codeGenerator.generate(someInput);
   IFile generatedFile = project.getFile("MyFile.java");
   assertTrue(generatedFile.exists());
   Lack of focus
   

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7. import org.eclipse.core.resources.IProject;
   !
   public class CodeGenerator {
   private IProject project;
   !
   public CodeGenerator(IProject project) {
   this.project = project;
   }
   !
   public void generate(Input input) {
   ...
   IFile file = project.getFile(someFileName);
   file.create(someContent, true, monitor);
   }
   !
   }
   Problem: Hard-wired dependency to Eclipse workspace
   

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8. public class CodeGenerator {
   private FileSystem fileSystem;
   !
   public CodeGenerator(FileSystem fileSystem) {
   this.fileSystem = fileSystem;
   }
   !
   public void generate(Input input) {
   ...
   !
   fileSystem.write(fileName, content);
   }
   !
   }
   public interface FileSystem {
   !
   void write(String fileName, String content);
   !
   }
   simpler implementation
   

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9. FileSystem fileSystem = new EclipseFileSystem("MyProject");
   CodeGenerator codeGenerator = new CodeGenerator(fileSystem);
   codeGenerator.generate(someInput);
   Eclipse
   Command Line
   Test
   MockFileSystem fileSystem = new MockFileSystem();
   CodeGenerator codeGenerator = new CodeGenerator(fileSystem);
   codeGenerator.generate(someInput);
   fileSystem.assertExists("SomeFile.java");
   JavaIOFileSystem fileSystem = new JavaIOFileSystem("~/MyProject");
   CodeGenerator codeGenerator = new CodeGenerator(fileSystem);
   codeGenerator.generate(someInput);
   this wasn’t possible before
   

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10. EclipseFileSystem
    CodeGenerator
    Problem: classes depending on implementation details
    

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11. FileSystem
    CodeGenerator
    EclipseFileSystem
    Dependency Inversion is your friend
    

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12. FileSystem
    CodeGenerator
    EclipseFileSystem
    ModelExporter
    ModelImporter
    Integration Test?
    …and here? …and here?
    

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13. FileSystem
    CodeGenerator
    EclipseFileSystem
    Interaction Test
    

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14. @Test public void writesGeneratedFilesToFileSystem() {
    FileSystem fileSystem = mock(FileSystem.class);
    CodeGenerator codeGenerator = new CodeGenerator(fileSystem);
    Input someInput = ...;
    CodeGenerator.generate(someInput);
    !
    verify(fileSystem).write("MyFile.java", "expected contents”);
    }
    

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15. Interaction Test
    FileSystem
    CodeGenerator
    EclipseFileSystem
    Contract Test
    

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16. public abstract class FileSystemContractTest {
    @Test public void writesContentToFile() {
    FileSystem fileSystem = createFileSystem();
    fileSystem.write("my_file.txt", "content");
    assertEquals("content", contentsOf("my_file.txt"));
    }
    !
    protected abstract FileSystem createFileSystem();
    !
    protected abstract String contentsOf(String file);
    !
    }
    public class JavaIoFileSystemTest extends FileSystemContractTest {
    @Rule public TemporaryFolder tempFolder = new TemporaryFolder();
    !
    @Override
    protected String contentsOf(String
    return Files.toString(tempFolder.newFile(fileName), UTF_8);
    }
    !
    @Override
    protected FileSystem createFileSystem() {
    return new JavaIOFileSystem(tempFolder.getRoot().getAbsolutePath());
    }
    !
    }
    public class JavaIoFileSystemContractTest extends FileSystemContractTest {
    !
    @Override
    protected String contentsOf(String fileName) {
    return Files.toString(fileName));
    }
    !
    @Override
    protected FileSystem createFileSystem() {
    return new JavaIOFileSystem(...);
    }
    !
    }
    

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17. Contract Interaction
    + Tests over Integration Tests.
    Favor
    

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18. #2 WRITE CLEAN TESTS
    

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19. public class PersonTest {
    @Test public void underAgePersonsAreNotAllowedToDrive() {
    Person underAgePerson = new Person(17);
    assertFalse(underAgePerson.isAllowedToDrive());
    }
    !
    @Test public void adultsAreAllowedToDrive() {
    Person adultPerson = new Person(18);
    assertTrue(adultPerson.isAllowedToDrive());
    }
    !
    @Test public void underAgePersonsAreNotAllowedToDrink() {
    Person underAgePerson = new Person(17);
    assertFalse(underAgePerson.isAllowedToDrink());
    }
    !
    @Test public void adultsAreAllowedToDrink() {
    Person adultPerson = new Person(18);
    assertTrue(adultPerson.isAllowedToDrink());
    }
    }
    

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20. public class PersonTest {
    @Test public void underAgePersonsAreNotAllowedToDrive() {
    Person underAgePerson = new Person(17);
    assertFalse(underAgePerson.isAllowedToDrive());
    }
    !
    @Test public void adultsAreAllowedToDrive() {
    Person adultPerson = new Person(18);
    assertTrue(adultPerson.isAllowedToDrive());
    }
    !
    @Test public void underAgePersonsAreNotAllowedToDrink() {
    Person underAgePerson = new Person(17);
    assertFalse(underAgePerson.isAllowedToDrink());
    }
    !
    @Test public void adultsAreAllowedToDrink() {
    Person adultPerson = new Person(18);
    assertTrue(adultPerson.isAllowedToDrink());
    }
    }
    Problem: ‘new’ couples implementation and test
    

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21. Avoid duplicated coupling between
    test and implementation.
    

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22. public class PersonTest {
    @Test public void underAgePersonsAreNotAllowedToDrive() {
    Person underAgePerson = new Person(17);
    assertFalse(underAgePerson.isAllowedToDrive());
    }
    !
    @Test public void adultsAreAllowedToDrive() {
    Person adultPerson = new Person(18);
    assertTrue(adultPerson.isAllowedToDrive());
    }
    !
    @Test public void underAgePersonsAreNotAllowedToDrink() {
    Person underAgePerson = new Person(17);
    assertFalse(underAgePerson.isAllowedToDrink());
    }
    !
    @Test public void adultsAreAllowedToDrink() {
    Person adultPerson = new Person(18);
    assertTrue(adultPerson.isAllowedToDrink());
    }
    }
    

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23. public class PersonTest {
    @Test public void underAgePersonsAreNotAllowedToDrive() {
    Person underAgePerson = createPerson(17);
    assertFalse(underAgePerson.isAllowedToDrive());
    }
    !
    @Test public void adultsAreAllowedToDrive() {
    Person adultPerson = createPerson(18);
    assertTrue(adultPerson.isAllowedToDrive());
    }
    !
    @Test public void underAgePersonsAreNotAllowedToDrink() {
    Person underAgePerson = createPerson(17);
    assertFalse(underAgePerson.isAllowedToDrink());
    }
    !
    ...
    !
    private void createPerson(int age){
    return new Person(age);
    }
    }
    

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24. public class PersonTest {
    @Test public void underAgePersonsAreNotAllowedToDrive() {
    assertFalse(anUnderAgePerson().isAllowedToDrive());
    }
    !
    @Test public void adultsAreAllowedToDrive() {
    assertTrue(anAdultPerson().isAllowedToDrive());
    }
    !
    @Test public void underAgePersonsAreNotAllowedToDrink() {
    assertFalse(anUnderAgePerson().isAllowedToDrink());
    }
    !
    private void anUnderAgePerson(){
    return new Person(17);
    }
    !
    private void anAdultPerson(){
    return new Person(18);
    }
    !
    private void createPerson(int age){
    return new Person(age);
    }
    }
    

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25. public class PersonTest {
    @Test public void underAgePersonsAreNotAllowedToDrive() {
    assertFalse(PersonBuilder.underAgePerson().build().isAllowedToDrive());
    }
    !
    @Test public void adultsAreAllowedToDrive() {
    assertTrue(PersonBuilder.adultPerson().build().isAllowedToDrive());
    }
    !
    @Test public void underAgePersonsAreNotAllowedToDrink() {
    assertFalse(PersonBuilder.underAgePerson().build().isAllowedToDrink());
    }
    !
    }
    

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26. public class CodeGenerationInWorkspaceTest {
    @Before
    public void cleanWorkspace(){
    Workspaces.clean();
    }
    ...
    !
    !
    }
    public class WorkspaceFileImportTest {
    @Before
    public void cleanWorkspace(){
    Workspaces.clean();
    }
    ...
    !
    }
    

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27. public class CodeGenerationInWorkspaceTest {
    @Before
    public void cleanWorkspace(){
    Workspaces.clean();
    Editors.closeAllOpen();
    }
    ...
    !
    !
    }
    public class WorkspaceFileImportTest {
    @Before
    public void cleanWorkspace(){
    Workspaces.clean();
    }
    ...
    !
    }
    

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28. Encapsulate test infrastructure setups.
    

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29. public class WorkspaceRule implements TestRule {
    !
    @Override
    public Statement apply(final Statement base, Description description) {
    return new Statement() {
    @Override
    public void evaluate() throws Throwable {
    clearWorkspace();
    base.evaluate();
    }
    };
    }
    private void clearWorkspace(){
    Workspaces.clean();
    Editors.closeAllOpen();
    }
    !
    }
    JUnit Rules FTW
    

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30. public class WorkspaceRule implements TestRule {
    !
    @Override
    public Statement apply(final Statement base, Description description) {
    return new Statement() {
    @Override
    public void evaluate() throws Throwable {
    clearWorkspace();
    base.evaluate();
    }
    };
    }
    private void clearWorkspace(){
    Workspaces.clean();
    Editors.closeAllOpen();
    }
    !
    }
    JUnit Rules FTW
    this runs the test
    

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31. public class CodeGenerationInWorkspaceTest {
    @Rule public WorkspaceRule workspace = new WorkspaceRule();
    !
    ...
    !
    }
    public class WorkspaceFileImportTest {
    @Rule public WorkspaceRule workspace = new WorkspaceRule();
    !
    !
    ...
    !
    }
    JUnit Rules FTW
    

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32. #3 LISTEN TO YOUR TESTS!
    

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33. How can I improve my design
    to make the test easier?
    When something is hard to test,
    ask yourself:
    

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34. Tests give you important feedback
    about your system’s design.
    - you just have to listen!
    

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35. THREE WAYS TO TAKE BACK CONTROL
    #1 Focus your tests
    #2 Write clean tests
    #3 Listen to your tests
    

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36. Recommended Reading
    - Growing Object-Oriented Systems guided by tests, Nat Pryce & Steve
    Freeman, http://www.growing-object-oriented-software.com
    - XUnit Test Patterns, Gerard Meszaros, http://xunitpatterns.com
    - Integration Tests are Scam, J. B. Rainsberger, http://www.infoq.com/
    presentations/integration-tests-scam
    - Subcutaneus Tests, Martin Fowler, http://martinfowler.com/bliki/
    SubcutaneousTest.html
    - Duplicated Test Code & High Coupling, Jason Gorman, http://
    codemanship.co.uk/parlezuml/blog/?postid=1182
    - Working Effectively with Legacy Code, Michael Feathers, http://
    www.amazon.com/Working-Effectively-Legacy-Michael-Feathers/
    dp/0131177052
    

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37. @sebabenz
    www.jnario.org
    E S R
    L A B S
    

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