What is the difference of BeforeAndAfter and BeforeAndAfterEach in ScalaTest

From scalatest documentation you can find all the info you need.

TL;DR: Both have the same functionality. BeforeAndAfter is more concise, while BeforeAndAfterEach is more stackable.

BeforeAndAfter recommended usage:

Use trait BeforeAndAfter when you need to perform the same side-effects before and/or after tests, rather than at the beginning or end of tests. Note: For more insight into where BeforeAndAfter fits into the big picture, see the Shared fixtures section in the documentation for your chosen style trait.

Should I use BeforeAndAfter or BeforeAndAfterEach? (From BeforeAndAfter perspective)

Although BeforeAndAfter provides a minimal-boilerplate way to execute code before and after tests, it isn't designed to enable stackable traits, because the order of execution would be non-obvious. If you want to factor out before and after code that is common to multiple test suites, you should use trait BeforeAndAfterEach instead.

The advantage this trait has over BeforeAndAfterEach is that its syntax is more concise. The main disadvantage is that it is not stackable, whereas BeforeAndAfterEach is. I.e., you can write several traits that extend BeforeAndAfterEach and provide beforeEach methods that include a call to super.beforeEach, and mix them together in various combinations. By contrast, only one call to the before registration function is allowed in a suite or spec that mixes in BeforeAndAfter. In addition, BeforeAndAfterEach allows you to access the config map and test name via the TestData passed to its beforeEach and afterEach methods, whereas BeforeAndAfter gives you no access to the config map.

BeforeAndAfterEach recommended usage:

Use trait BeforeAndAfterEach when you want to stack traits that perform side-effects before and/or after tests, rather than at the beginning or end of tests. Note: For more insight into where BeforeAndAfterEach fits into the big picture, see the Shared fixtures section in the documentation for your chosen style trait.

Should I use BeforeAndAfter or BeforeAndAfterEach? (From BeforeAndAfterEach perspective):

The main advantage of BeforeAndAfterEach over BeforeAndAfter is that BeforeAndAfterEach. enables trait stacking. The main disadvantage of BeforeAndAfterEach compared to BeforeAndAfter is that BeforeAndAfterEach requires more boilerplate. If you don't need trait stacking, use BeforeAndAfter instead of BeforeAndAfterEach. If you want to make use of test data (the test name, config map, etc.) in your beforeEach or afterEach method, use trait BeforeAndAfterEachTestData instead.

P.s. I see that there is a common mistake that one will execute for each test and the other won't. There is another trait for that called BeforeAndAfterAll.

As the name suggest BeforeAndAfter will run once(at start and at the end) for a test class. BeforeAndAfterEach will run before and after each test case in the class.

Use BeforeAndAfter: Suppose you want you create an in Memory database for the tests to run you will create it before running the test cases and then you will clear the memory after running all the test cases.

Use BeforeAndAfterEach: Suppose you have some cache value which requires different value for each test case to run, in that case you can change the value of that cache for before each test case and clear it after running a single test.