1. A system, comprising: a physical computer system comprising: a processor; and a memory coupled to the processor, wherein the memory is configured to store instructions executable by the processor to implement a virtualization module, wherein the virtualization module is configured to present a virtualized computing service application programming interface (API) to one or more clients that are external to the virtualization module, wherein the virtualized computing service API is configured to receive client requests for virtualized computing services to be performed on behalf of the one or more clients; wherein the virtualization module is configured to: in response to a client request received via the virtualized computing service API, implement one or more virtual machines, wherein each of the one or more virtual machines is configured to execute an operating system that is distinct from any underlying operating system executed by the physical computer system; in response to a client request received via the virtualized computing service API to perform an initial execution of a computation that has been identified as a repeatable computation expected to reproduce one or more results of the initial execution when re-executed, instruct that the one or more virtual machines perform the repeatable computation to generate an original terminal state of the repeatable computation; subsequent to generation of the original terminal state and in response to a client request to repeat the repeatable computation, instruct that the one or more virtual machines perform the identified repeatable computation to generate a new terminal state of the repeatable computation; and dependent upon a comparison of the original terminal state and the new terminal state, determine whether the repeatable computation has been successfully repeated according to a success criterion.