1. A computer-implemented method of testing software comprising: identifying, at a first point in time, first code that has been modified; identifying, using first mapping information, a testing set of one or more test cases wherein the first mapping information identifies each test case of the testing set as a test case used to test the first code, wherein said first mapping information is generated based on runtime code coverage information obtained from previously executing each test case of the testing set; running the testing set, wherein said running includes executing second code in accordance with the testing set; generating coverage information in accordance with said executing the second code; analyzing the coverage information; generating second mapping information in accordance with said analyzing of the coverage information generated as a result of executing the second code; updating the first mapping information in accordance with the second mapping information; identifying, in accordance with the second mapping information, at least one code entity of the first code that is not covered by at least one test case whereby the second mapping information indicates that there is no current test case for testing the at least one code entity, wherein the at least one code entity of the first code not covered by at least one test case includes a first code entity; adding a new test case to test the first code entity; executing code in accordance with the new test case; generating second coverage information in accordance with said execution in accordance with the new test case; analyzing the second coverage information; generating third mapping information in accordance with said analyzing the second coverage information; and updating the first mapping information in accordance with the third mapping information, said third mapping information identifying the new test as causing execution of the first code entity; and responsive to a first trigger event, performing other processing comprising: identifying an existing test case without mapping information wherein no code is identified as being executed by the existing test case; responsive to identifying the existing test case without mapping information, executing the existing test case and determining what code is executed by the existing test case; and generating, in accordance with said executing, additional mapping information for the existing test case, said additional mapping information identifying what code is executed by the existing test case.