I don’t do it on purpose but sometimes it can be so much fun to dive into an exception you’ve never seen before. You always come out with some new acquired wisdom. It all started with the following exception during the execution of our unit tests: System.InvalidOperationException : Operations that change non-concurrent collections must have exclusive access. A concurrent update was performed on this collection and corrupted its state. The collection's state is no longer correct. A look at the stacktrace brought us to the initialization system of our application where multiple modules are configured and initialized: at System.Collections.Generic.Dictionary`2.TryInsert(TKey key, TValue value, InsertionBehavior behavior) at System.Collections.Generic.Dictionary`2.set_Item(TKey key, TValue value) at SOFACore.EntityFramework.EntityFrameworkModule.Initialize(IServiceCollection services) in /_/SOFACore/SOFACore.EntityFramework/EntityFrameworkModule.cs:line 30 Inside this mo...