Testing a MassTransit Consumer using the InMemoryTestFixture

In your test fixtures, I don't believe there should be any conflict, but because of the interaction with NUnit, there may be something of which I'm unaware because of the base class inheritance that's being used.

If you use the InMemoryTestHarness directly (the same functionality as the text fixtures, but without any testing framework dependency) I would expect that you should not experience any interactions between two simultaneously executing tests.

Your approach is the way it should be done, but again, I'd suggesting using the InMemoryTestHarness instead of the fixture.

An example test is linked: https://github.com/MassTransit/MassTransit/blob/master/src/MassTransit.Tests/Testing/ConsumerTest_Specs.cs