2. Reliability
It measured in the way that refers to as test/re-test reliability to distinguish it from mark/re-mark reliability. The test that has reliability should have the extent simple of material for testing. The next one is the administration of the test that means same test administered to different groups under different conditions or at different times.
In my test, I have the sample item for tester to see first and my test try to use the instruction that is clearly for tester.
3. impact
It is its capacity to discriminate among the different candidates and to reflect the difference in the performance of the individuals in the group. The extent of need to discriminate will vary depending on the purpose of the test.