private int getOplogFileSizeSum(File dir, String type) {
    int sum = 0;
    File[] files = dir.listFiles();
    for (File file : files) {
      String name = file.getName();
      if (name.endsWith(type)) {
        sum += file.length();
      }
    }
    return sum;
  }
Tests reduction in size of disk stats when the oplog is rolled.
geode-core/src/integrationTest/java/org/apache/geode/internal/cache/OplogJUnitTest.java