Trying to use the Test Explorer with Ix.NET, I see the tests show up momentarily and then disappear.

I've tried this with 15.2.2 and 15.3 preview 2.

To repro:
Clone https://github.com/Reactive-Extensions/Rx.NET,
Checkout develop, fa19894bb71a902f44feb3cc2df62895d3cdaf75
Open up Ix.NET\source\Ix.NET.sln and build

Tests aren't showing up in the test explorer window