There are many unit test temporary files left behind after test runs. In the case of CI servers, I have seen >70,000 files accumulate in /tmp over a period of time. Each unit test should make an effort to remove its temporary files when the test is completed.
My current unit test cleanup block:
# clean up after unit tests..
rm -rf /tmp/140*-0 /tmp/CFWith* /tmp/Counter1* /tmp/DescriptorTest* /tmp/Keyspace1* \
/tmp/KeyStreamingTransferTestSpace* /tmp/SSTableExportTest* /tmp/SSTableImportTest* \
/tmp/Standard1* /tmp/Statistics.db* /tmp/StreamingTransferTest* /tmp/ValuesWithQuotes* \
/tmp/cassandra* /tmp/jna-* /tmp/ks-cf-ib-1-* /tmp/lengthtest* /tmp/liblz4-java*.so /tmp/readtest* \
/tmp/set_length_during_read_mode* /tmp/set_negative_length* /tmp/snappy-*.so