synchronized int increaseVersion() {
        return ++version;
    }
@Test
    void increaseVersion() {
        Job job = anEnqueuedJob().build();
        assertThat(job.getVersion()).isZero();

        assertThat(job.increaseVersion()).isEqualTo(1);
        assertThat(job.getVersion()).isEqualTo(1);

        assertThat(job.increaseVersion()).isEqualTo(2);
        assertThat(job.getVersion()).isEqualTo(2);
    }