Create example for TemporaryFolder extension

What would an implementation outline look like?

Usage:

@ExtendWith(TemporaryFolder.class)
public class TempTest {
// ...
  @Test
  void temp(@TemporaryFolder.Tag TemporaryFolder temp) throws IOException {
    System.out.println(temp.getRoot());
  }
}

Implementation (“copied” from JUnit 4, stripped ExternalResource dependency):

public class TemporaryFolder implements MethodParameterResolver, AfterAllExtensionPoint {

  @Target(ElementType.PARAMETER)
  @Retention(RetentionPolicy.RUNTIME)
  public @interface Tag { }
// ...
  @Override
  public Object resolve(Parameter parameter, MethodInvocationContext mci, ExtensionContext ec)
      throws ParameterResolutionException {
    try {
      create();
    } catch (IOException e) {
      throw new ParameterResolutionException(e.toString());
    }
    return this;
  }

  @Override
  public boolean supports(Parameter parameter, MethodInvocationContext mci, ExtensionContext ec)
      throws ParameterResolutionException {
    return parameter.isAnnotationPresent(Tag.class);
  }

  @Override
  public void afterAll(ContainerExtensionContext arg0) throws Exception {
    delete();
  }
}

[mniedero]

Indeed, it would be great if there is a replacement of JUnit 4 TemporaryFolder within JUnit 5.

Here, I’ve re-engineered lot of JUnit tests for following reasons: o) make them platform independent (Win/Linux). We develop on Windows but Jenkins CI is running on Linux (RHEL 7 like) o) have a testbed that is celeaned-up/destroyed automatically after success. This is essential on Jenkins CI because I’m interesseted to minimize time needed for maintenance as much as possible. o) lot of my tests are like integration test: They read and write files. But, writing files into folder structure containing source code is strictly forbidden.

Well, I can write my own TemporaryFolder code like ten years (or more) ago. Since a Temporaryfolder rule is available with JUnit 4 this is no longer feasible. For the moment, missing TemporaryFolder Extension is biggest hurdle for migration from Junit 4 to JUnit 5. No, it has become a no-go.

[sormuras]

It only took you (now: us) two years and a couple of month!

🥂