SpecFlow feature not found by Visual Studio Test Explorer

I'm following a course on SpecFlow and have installed SpecFlow via extensions into VS2013 Ultimate, and added SpecFlow and NUnit to the current Class Library project. After creating a feature, and building successfully, the scenarios do not show up in Test Explorer as expected. I've restarted Visual Studio, cleaned and rebuilt, nothing causes the scenarios to show up in Test Explorer.

Any tips?

Feature: SpecFlowFeature1

@mytag
Scenario: Scenario A
    Given X
    When Y
    Then Z

Scenario: Scenario B
    Given X
    When Y
    Then Z

Scenario: Scenario C
    Given X
    When Y
    Then Z