How extensive tests should be is debatable. Striving for 100% code coverage does not necessarily mean that a block of code has been effectively tested.

Consider testing the following:

• Parameters
• Any complex conditions
• Acceptance of different input or expected values, including complex parameter validation
• Exit conditions (especially raised errors or exceptions)

When writing a unit test, resist the temptation to test other functions or commands. A unit test is not responsible for making sure that every command that it calls works. That comes later.