1. A method for asynchronous code testing, said method comprising: generating, by a processor of a computer system, test cases from an input code that comprises code blocks organized in a hierarchy of nesting levels characterized by respective nesting level numbers that increase with increasing separation of each respective nesting level from a reference level of the total input code, wherein each test case comprises a respective launching priority that quantifies how strongly each test case is associated with at least one modified code block of the input code, and wherein said generating the test cases comprises determining the respective launching priority for each test case by (i) determining an association strength of each modified code block as measured by the nesting level in the hierarchy of each modified code block such that the association strength decreases as the nesting level increases for each modified code block and (ii) computing the launching priority as a sum of the association strengths of the modified code blocks; and said processor producing a test run result by asynchronously running the test cases in a sequential order of increasing launching priority of the test cases.