The order in which commands appear in the command tree is significant. Commands should be sorted such that if command A depends on command B, then B will appear before A in a pre-order traversal of the tree.

The ordering constraint is intended to simplify the implementation of ITestDrivers. Test drivers may assume that executing ITestCommands in pre-order traversal sequence will be sufficient to ensure that all dependencies can be evaluated in time.

However, a ITestDriver is not required to run the tests in the specified order. Moreover, it is not required to run them serially at all. (In fact, it is not even required to use this API.) A smart ITestDriver might run tests in parallel or take into account additional sequencing constraints governing execution order.

In order to achieve correct behavior, a ITestDriver should satisfy the following guarantees with respect to test commands:

• A test command runs within the scope of its parent test command.
• A test command runs only after all of the test commands it depends on have passed.
• A test command with a failed dependency or that is not run for internal reasons reports a test outcome of Skipped.