test: background work inline, shared mock bases, lock-wait instead of sleep

readme.md

@@ -437,6 +437,10 @@ Configuration comes from environment variables:
 ```
 
 Runs unit, WebMvc, persistence and integration tests plus the ArchUnit rules. Needs Docker for Testcontainers.
+In integration tests background work runs on the calling thread, so a test reads the result at once.
+`AbstractMockedAdaptersTest` mocks Steam, IGDB and speedrun.com, `AbstractMockedLibraryServicesTest` the sync and
+the refreshes of the picker and stats pages; each is one shared Spring context. Race tests wait until the other
+connection waits for the row lock (`awaitLockWaiter`), not for a fixed time.
 
 ## Roadmap