1. Computer apparatus for developing load tests of a computing system, the apparatus having an existing protocol and comprising: a kernel in memory providing a plurality of core actions for use in a subject load test script, core actions employed in the subject load test script being implemented as respective atomic kernel actions that are specializations of the corresponding core actions that can be executed at will, the kernel being written in an object-oriented programming language underlying the existing protocol of the apparatus such that each individual kernel action is modeled as a respective object in the object-oriented programming language enabling different kernel actions to be treated equally in execution resources, and each kernel action being atomic and extensible; an execution engine in working memory executed by a processor and applying the subject load test script to a number of test clients, the execution engine as executed by the processor scheduling for execution and executing the kernel actions, the kernel actions being able to be swapped into and out of executable states and individually executed at will and treated equally enabling a number of resources per number of kernel actions instead of per number of test clients, and resulting in use of a relatively small number of resources as compared to the number of test clients, wherein the relatively small number of resources is less than one thread per user emulated to generate a load, wherein the processor is free from creating a process for each test client and wherein the processor enables a plurality of kernel actions of different test clients in one process; and an extender in memory operatively communicating with the kernel and extending the protocol including any combination of extending base classes of the protocol and adding features to the protocol, the kernel enabling the subject load test script to be responsive to extensions of the protocol and adding corresponding references to the test script to be run resulting in, for a given kernel action, a new kernel action being executed in place of the given kernel action free of necessitating modification of the rest of the kernel.