I initially ignored that article since I'm using the new OpenAccesContext. I'd did put me in the right direction though, thanks.
A bit of searching made me find a protected method which allows me to get the ObjectScope. That allowed me to dispose the scope and the attached database. Now I can delete the database file between tests.
For those interested, this the code in my test tear down:
OaModel ctx =
MethodInfo m = ctx.GetType().GetMethod(
, BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic);
IObjectScope scope = (IObjectScope)m.Invoke(ctx,