Junit5: Provide support for setting a custom parent directory for @TempDir

[rkrisztian]

My project requires that I do not write to /tmp or whichever location it is when I use the TempDirectory extension. So right now I have no choice but to still use junit-pioneer's implementation, e.g. like this:

```java
@RegisterExtension
Extension tempDirectory = TempDirectory.createInCustomDirectory(() -> Paths.get("build"));

@BeforeEach
void setup(@TempDir Path testProjectDir) {
// Do something with "testProjectDir".
}
```

But it would be nicer if I could just use stock JUnit 5 for this. JUnit 4 supported setting the parent dir, so I find the JUnit 5 way a bit too limiting.

Thanks in advance.

[sbrannen]

Tentatively slated for 5.6 M2 solely for the purpose of _team discussion_

[marcphilipp]

If your project requires you not to write to the default location of temporary files, you should set the java.io.tmpdir system property.

@rkrisztian Could you please try that?

[rkrisztian]

Worked, thanks! I wish I knew about this. :)

[sbrannen]

Assigned to the general backlog and labeled as waiting for interest.

[rkrisztian]

FYI: A co-worker of mine suggested the use of AbstractTask#getTemporaryDir():

tasks.withType(Test) {
  systemProperty 'java.io.tmpdir', temporaryDir
}

[dariocutillas]

I'm also interested in this functionality.

In my case I only want to affect the parent directory of one @TempDir and therefore it does not make sense to use java.io.tmpdir.