CODEWITHSUNDEEP
java
user9547680
user9547680

Reputation: 33

Access private method of an instance in unit test

I came across the following issue when I was trying to unit test my code. If I have a class that creates an instance and for example a getter method like this:

public class Test {

   private static Test instance;
   private ArrayList<String> arrayList = new ArrayList<String>();

   public  static Test getInstance() {
      return instance;
   }

   private ArrayList<String> getArrayList() {
      return arrayList;
   }
}

If now I want to access the arrayList in a test case it would fail, because the list is returned by a non-accessable private method. So trying something like this wouldn't work:

public class AccessTest {

   private Test test;

   public void accessList(){
      test = Test.getInstance();
      test.getArrayList();
   }
}

So one way to access the arrayList anyway, would probably be to change the visibility to protected. But isn't there a better way to access the method? Is it really necessary to make a method protected only because of a test that needs to access it?

Upvotes: 0

Views: 2137

Answers (3)

mate00
mate00

Reputation: 2955

In general, if you have some private methods in your class and you feel that you have problems with testing them, it is a sign of a bit of a code smell. It shows that too many functionality is hidden behind private wall.

You could change visibility of such method to package protected, so JUnit test will see it. There is also a Google Guava annotation @VisibleForTesting or something like that. But again - this is a sign of wrong class design.

Think of extracting such method to a separate class and make that methods public then.

For example, take a look at the following code:

class ReportCreator {
  public File createSomeImportantReport(LocalDate date) {
    String fileName = provideFileName(date);
    File result = new File(fileName);
    return result;
  }

  private String provideFileName(LocalDate date) {
    // ... some complex business logic to generate file name based on date... ;)

    return fileName;
  }
}

There is a private method provideFileName() that does some complicated things and let's say it's hard to test if you would test only createSomeImportantReport().

See what changes if you externalize that functionality.

class ReportCreator {
  private FileNameProvider fileNameProvider;

  public File createSomeImportantReport(LocalDate date) {
    File result = new File(fileNameProvider.provideFileName(date));
    return result;
  }
}

class FileNameProvider {
  public String provideFileName(LocalDate date) {
    return ......;
  }
}

You now have option to test that thing separately, focus on what's important in that particular case.

Upvotes: 5

SBylemans
SBylemans

Reputation: 1764

Despite the fact that I don't see a use case for a private getter, you can use the package private access level. This is the default access level so you don't have to specify it. You can then test it by adding the test class in the same package name in the test directory. For instance the class is located in src/main/java/application and the test class can then be located in src/test/java/application.

Upvotes: 2

Jeremy Then
Jeremy Then

Reputation: 535

Use Java Reflection for that:

Test test = new Test();

Method getArrayListMethod = test.getClass().getDeclaredMethod("getArrayList", null);

getArrayListMethod.setAccessible(true);

ArrayList<String> list = (ArrayList<String>) getArrayListMethod .invoke(test);

System.out.println(list); // Prints the list

Create your Test object, use the method getClass() and get the method declared on that class by its name. Then set that method accessible dynamically. If you know the data type that it returns, then cast it to it.

Upvotes: 0

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