What does blue '?' over green mark mean in Unit Test Session window in VS 2012?

Question

Here is the printscreen. Cannot find the answer what these questions mean.

Update.

Found the answer. Which is quite simple. Will leave it here for those who may be interested.

Question mark denotes that particular test was not run the last time unit tests were started.

Update. This UI is due to installed Resharper.
In clean Studio not run tests become grayed.

Answer 1

Question mark denotes that particular test was not run the last time unit tests were started.

So this means that depicted result ma have changed.