What makes a Visual Studio project a test project?

Question

I just tried to open one of my load tests and I'm greeted with:

But this is the test project. Why is Visual Studio not treating it as one?

Update 1:

I found this two statement in the csproj which where not pointing the the correct location and corrected it.

…
  <Import Condition="Exists('..\packages\MSTest.TestAdapter.2.2.4\build\net45\MSTest.TestAdapter.props')" Project="..\packages\MSTest.TestAdapter.2.2.4\build\net45\MSTest.TestAdapter.props">
  </Import>
…
  <Import Condition="Exists('$(VSToolsPath)\TeamTest\Microsoft.TestTools.targets')" Project="$(VSToolsPath)\TeamTest\Microsoft.TestTools.targets">
  </Import>
…
  <Import Condition="Exists('..\packages\MSTest.TestAdapter.2.2.4\build\net45\MSTest.TestAdapter.targets')" Project="..\packages\MSTest.TestAdapter.2.2.4\build\net45\MSTest.TestAdapter.targets">
  </Import>
…

Update 2:

The test project type is set to WebTest — which seems correct:

…
    <TestProjectType>WebTest</TestProjectType>
…