### Question:
SnapshotFile { @VisibleForTesting static String createSnapshotFileName(String serverName, long index) { return String.format("%s-%d.%s", serverName, index, EXTENSION); } SnapshotFile(File file, File temporaryFile); static boolean isSnapshotFile(File file); File file(); String name();  }### Answer:
@Test public void testCreateSnapshotFileName() throws Exception { assertEquals("test-1.snapshot", SnapshotFile.createSnapshotFileName("test", 1)); assertEquals("test-2.snapshot", SnapshotFile.createSnapshotFileName("test", 2)); }