1. A carrier medium comprising program instructions executable to: include a plurality of test executive steps in a test executive sequence in response to user input, wherein each test executive step includes control functionality implemented by a test executive engine; configure each of the test executive steps to call a user-supplied code module in response to user input; and execute the test executive sequence under control of the test executive engine, wherein said executing comprises the test executive engine executing each of the test executive steps in the test executive sequence; wherein for each test executive step in at least a subset of the test executive steps in the test executive sequence, the test executive engine is operable to: execute the control functionality of the test executive step in a first process; and invoke the user-supplied code module called by the test executive step for execution in a different process other than the first process.