For learning unit tests I would try doing radical TDD for few weeks. Radical, as in not writing a single line of code, unless you have a test that fails when the line is not there. It will be weird at first - you will spend more time thinking about writing tests than about writing code. But pretty fast you will develop a sense of what is easy to test and what is not
Recovering interrupter with occasional relapses, lover of spreadsheets, blogger, programmer, adept debugger, conjurer of analogies, and probably other things.
For learning unit tests I would try doing radical TDD for few weeks. Radical, as in not writing a single line of code, unless you have a test that fails when the line is not there. It will be weird at first - you will spend more time thinking about writing tests than about writing code. But pretty fast you will develop a sense of what is easy to test and what is not
I did that for a brief stint, and it really helped me develop that sense you mention.