1. A computerized apparatus for generating a testcase, the computerized apparatus having a processor and a storage device, the computerized apparatus comprising: a test template obtainer operative to obtain a test template associated with a system-under-test (SUT), wherein the SUT comprises a plurality of units, wherein the test template represents alternative testcases in which the plurality of units interact, a system-level generator operative to generate an abstract testcase based on the test template, wherein said system-level generator is operative to perform system-level generation tasks defined by the test template; and at least one unit-level generator operative to generate a testcase comprising the abstract testcase, wherein said at least one unit-level generator is operative to perform unit-level generation tasks defined by the test template.