In SDLC, after completing the design doc, we have to prepare Unit Test cases.
UNIT TEST CASE doc is nothing but defining test cases for the required functionality unit wise. Like verifying all exceptions..(file open/clsoe/read/write....If cond/While cond & also for some functional validation). Test case should contain test scenario & expected outcome. During test case, we will ptrepare the test data as well.
After CODING phase, we will execute our object & verify the results according to the TEST CASE we written earlier.