final Properties properties = new Properties();
properties.setProperty("prop1", "value1");
properties.setProperty("prop2", "value2");
properties.setProperty("prop3", "value3");
properties.setProperty("prop4", "value4");
final ResourcePreProcessor processor = new PlaceholderProcessor().setPropertiesFactory(WroUtil.simpleObjectFactory(properties));
final URL url = getClass().getResource("placeholder");
final File testFolder = new File(url.getFile(), "test");
final File expectedFolder = new File(url.getFile(), "expected");
WroTestUtils.compareFromDifferentFoldersByExtension(testFolder, expectedFolder, "css", processor);