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?You should 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.
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.