### Question:
RunIdSequence { public RunId nextRunId() { int currentId = nextId.getAndIncrement(); return new RunId(currentId); }  RunId nextRunId();  }### Answer:
@Test public void starts_from_the_first_RunId() { assertThat(sequence.nextRunId(), is(new RunId(RunId.FIRST_ID))); }
@Test public void each_subsequent_RunId_is_incremented_by_one() { RunId id0 = sequence.nextRunId(); RunId id1 = sequence.nextRunId(); RunId id2 = sequence.nextRunId(); assertThat(id1.toInt(), is(id0.toInt() + 1)); assertThat(id2.toInt(), is(id1.toInt() + 1)); }