Hi, thanks for posting.

The easiest way to understand this is to take a look at the Processing Queue Window when you have NCrunch running inside Visual Studio.

Inside this window, you'll see a list of test tasks that are being executed more or less in sequence by the engine, with some degree of parallelisation depending on your settings.

Each test task is an effective grouping of tests that are passed into the test framework as a batch, and are therefore run together within the same process. After a batch has been completed, the process used to execute them will be re-used (if possible) for later batches in the run.

By default NCrunch considers tests distinct from their fixture and will allow two tests to be run in parallel with each other under the same fixture. Usually, this is not a problem as long as the tests don't share state outside the test process (i.e. the file system or a database, etc). Where you want to avoid parallel execution of tests under their fixture, you can suppress this by specifying NCrunch.Framework.ExclusivelyUsesAttribute or NCrunch.Framework.AtomicAttribute on the parent fixture.

Terminology:
"Process": A physical .EXE process running under windows, visible in Windows Task Manager.
"Processing Thread": A logical task worker under NCrunch. The Max Number Of Processing Threads determines the number of tasks in the processing queue that can run at the same time. This is not the same as a physical thread under Windows, since a physical thread is contained inside inside a single process (.exe).
"Test Runner": A sandboxed integration adapter that ties into a test framework and drives it to run tests. Under NCrunch, the test runner is housed inside satellite .EXEs under the name nCrunch.TestHost.{Platform}.{FrameworkVersion}.exe.

Correct.



Correct. This is an important consideration for fixtures containing tests that must be run in the same fixture and in a specific sequence. Where this exists, you definitely want to use AtomicAttribute.



Yes and no. When a fixture is 'Atomic', its tests cannot be separated from the fixture or from each other, so they are always placed in the same task. However, this task does not need to be limited to just the atomic fixture. It's legal for this task to also contain other tests. If you need the fixture and its tests to be run in complete isolation in their own process, you can use NCrunch.Framework.IsolatedAttribute.