I have had problems when writing functional tests using Director::test()
Because the test made for a shared module needs to be independent of theme templates I want to force it to use a template in the module. But because theme templates overrides the module template my tests does not know what to expect.

Did anyone face the same problem and come up with a solution?

A collegue had this simple but brilliant idea when working on something entirely different.
By setting theme in SSViewer to null during test setup we force Director::test() to use eigther the template in the tested module or in mysite. Given that we're testing ajax or a pagetype of course.

public function setUp() {
  SSViewer::set_theme( null );
}

public function tearDown() {
  SSViewer::set_theme( SSViewer::current_custom_theme() );
}

public function testTemplate() {
  $responseByTemplateInModule = Director::test("/mypage");
}