Long answer :We have categorized tests into various categories - Standard Tests and (optionally) Practice Tests, Objective-wise Tests, and Leitner Mode.
Standard Tests are meant to cover all the questions in the question bank. That is, if you take all the Standard Tests, you would see all the questions in the question bank. Practice Tests select random questions of a particular toughness level from the same question bank. Objective wise tests select random questions of any toughness level from the same question bank. Leitner mode is an entirely different style of attempting the same questions in the question bank.
Each Standard Test is unique among Standard Tests. That is, no question is repeated in Standard Tests. However, if you take any other kind of test after taking all the Standard Tests, you will not see any new question. Similarly, if you mix tests of different categories, some question will be repeated. For example, if you take a Practice Test or an Objective-wise test, or a test in Leitner Mode after taking a Standard Test, you may see questions that you have already seen in the Standard Test. Also, since Practice Tests and Objective wise Tests pick questions randomly from the question bank, if you take a Practice Test or an Objective-wise Test multiple times, some questions will be repeated.
So which mode should I use?
Generally, students judge their level of preparation by the scores they get on the mock exams. But these scores will not be able to indicate that correctly, if the student has already seen all/some of the questions. Since practice/objective wise tests select questions randomly from the same set of questions, if you take Standard Tests after taking practice/objectivewise tests, you may already know answers to some of the questions and so, your score on the standard tests may not reflect your preparation level accurately.That is why we suggest that you take only the tests that match the mode of your preparation. For example, if you are done with your studies, you should only take the Standard Tests one by one. If you are going through a book and want to solidify your understanding of a particular chapter/objective, you may use the Objective-wise tests. If you want to check if you are an expert or not, you may use Practice Tests. But if you take Practice/Objective wise tests, do not rely on the scores to judge if you are ready for the real exam or not.
If your question bank contains "Last Day Test (Unique)", you may take this test even after taking other tests because questions in this test are explicitly excluded from all other tests (except Leitner Mode). This is done so that even if you take Practice tests or Objective wise tests, you will still have one Standard Test which will give you a true picture of your preparation.
For the same reason, you should not take a Standard Test more than once because a Standard Test contains preset questions and if you take the test again, you will get the same questions. The score that you get will therefore not indicate your true level of preparation.