Session driver failing in application test

I'm trying to create an application test, and I'm inserting some data into the session. Since we are using phpunit with the default config, the session driver is "array".

When I have a test class with a single test method, and pump some data into my session, the test works as expected. When I add another test method (even with nothing in it!), I get an exception about a view complaining that the "errors" variable is not defined, even though I am running the test with middleware. I have verified that the ShareErrorsFromSession middleware is firing.

Any advice/help appreciated