Review: [MERGE] Convert test.blackbox.test_c* to use internals where appropriate

[Martin Pool]

Martin Pool has voted approve.
Status is now: Semi-approved
Comment:
Looks reasonable and previously approved, will merge.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C1188468535.29725.8.camel%40lapbert%3E