xunit test can not be found or the problem is not available testhost test solution

xunit test, several packages need to be installed as follows:

1. Microsoft.TestPlatform.TestHost
2. Microsoft.NET.Test.Sdk
3. xunit.runner.visualstudio
4. xunit

1 and 2 will not install can not find testhost, do not install third problem can occur tests did not find.

Further, the test should be placed in a special class of test items, rub together can cause problems with a plurality of entry points (main function).