set("a", "a", "a")
    set("b", "b", "b")

    // We can't begin the edit if writing 'DIRTY' fails.
    filesystem.setFaultyWrite(journalFile, true)
    assertThat(cache.edit("c")).isNull()

    // Once the journal has a failure, subsequent writes aren't permitted.
    filesystem.setFaultyWrite(journalFile, false)
    assertThat(cache.edit("d")).isNull()