A test execution report should include a summary of the test execution results, the system/application under test and its version, and the environment in which the tests have been executed. These elements are essential to understand the context and outcomes of the testing process fully. Defect clusters identified during test execution are not typically part of a test execution report; they are more relevant to a defect or bug report, which focuses specifically on the faults and issues found during testing rather than the overall execution results.