Use the triple-equal operator to produce informative test failure messages.

Suppose I asserted that element.width === 3, then I would get a test
failure message of "4 did not equal 3", with just this code.
Use the expectResult method to produce better failure messages.

The failure message for a failed expectResult yields a failure message
of "expected X, but got Y".
Add an example showing the intercept test function used to expect exceptions.