public boolean usable() {
        if (path.toFile().exists()) {
            return updateValues(time.milliseconds());
        } else {
            LOG.debug("Disabling IO metrics collection because {} does not exist.", path);
            return false;
        }
    }
@Test
    public void testUnableToReadNonexistentProcFile() throws IOException {
        TestDirectory testDirectory = new TestDirectory();
        Time time = new MockTime(0L, 100L, 1000L);
        LinuxIoMetricsCollector collector = new LinuxIoMetricsCollector(testDirectory.baseDir.getAbsolutePath(), time);

        // Test that we can't read the file, since it hasn't been written.
        assertFalse(collector.usable());
    }