Generates one row in a standard-format table of tests of a dialog action.
First unnamed parameter is the name of the start page of the test. Second unnamed parameter, which may be omitted but omission is not recommended, describes the test, in the second column of the table. Optional parameter
test names am experimental version of the action to use in the test.
If the start page of the test exists, a button is provided to start the test. If the start page of the test does not exist, instead a button is provided to create it.
It's important the button to start a test is not delegable, to avoid imposing spurious state on the test from previous dialog; and when the do action itself is being tested, the button uses parameter
rescript to purge cached old versions of functions.