Don Libes is also the author of "Obfuscated C Code and Other Mysteries", which is the first book I ever read that really explores all the dark corners of programming in C; it's a really great book if you use the C language.

I used Expectk extensively in 1993, but I can't say I really enjoyed it. It was a crufty and error-prone undertaking, and in my opinion is best for testing, or as a last resort for talking to black-box code with an interactive cli.