One Test Only, Please
Minimize the number of tests that depend on a particular piece of functionality such that each test condition is covered by exactly one test. Tests that verify the same functionality will usually fail at the same time and require the same maintenance when the functionality is modified. Give attention to tests that verify the same code in different ways as these may indicate different test conditions. Avoid Eager Tests that verify too many test conditions. Picking the right tests is essential in employing a risk-based approach to testing.
*Above title should be read with a Scottish/Russian accent (think Sean Connery - Red October).