public function testCleanThemeRelatedContent()
 {
     $themeMock = $this->getMockBuilder('Magento\\Framework\\View\\Design\\ThemeInterface')->getMockForAbstractClass();
     $eventMock = $this->getMockBuilder('Magento\\Framework\\Event')->disableOriginalConstructor()->getMock();
     $eventMock->expects($this->any())->method('getData')->with('theme')->willReturn($themeMock);
     $observerMock = $this->getMockBuilder('Magento\\Framework\\Event\\Observer')->disableOriginalConstructor()->getMock();
     $observerMock->expects($this->any())->method('getEvent')->willReturn($eventMock);
     $this->themeConfig->expects($this->any())->method('isThemeAssignedToStore')->with($themeMock)->willReturn(false);
     $this->themeImageFactory->expects($this->once())->method('create')->with(['theme' => $themeMock])->willReturnSelf();
     $this->themeImageFactory->expects($this->once())->method('removePreviewImage');
     $this->updateCollection->expects($this->once())->method('addThemeFilter')->willReturnSelf();
     $this->updateCollection->expects($this->once())->method('delete');
     $this->themeObserver->execute($observerMock);
 }