Currently, various tests use LegacyScriptPubKeyMan because it was convenient for the refactor that introduced the ScriptPubKeyMan interface. However, with the legacy wallet slated to be removed, these tests should not continue to use LegacyScriptPubKeyMan as they are not testing any specific legacy wallet behavior. These tests are changed to use DescriptorScriptPubKeyMans.
Some of the coin selection tests and benchmarks had a global testWallet, but this seemed to cause some issues with ensuring that descriptors were set up in that wallet for each test. Those have been restructured to not have any global variables that may be modified between tests.
The tests which test specific legacy wallet behavior remain unchanged.