private long randBetween(long a, long b) {
    long x = a + randLong(b - a + 1);
    assertTrue(a <= x && x <= b);
    return x;
  }
Disable this when this test fails hopelessly and you need to debug a simpler case.
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestSeekOptimizations.java