问SpecFlow没有在工具->选项->SpecFlow->TestRunnerTool中列出NUnit

EN

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <configSections>
    <section name="specFlow" type="TechTalk.SpecFlow.Configuration.ConfigurationSectionHandler, TechTalk.SpecFlow" />
  </configSections>
  <specFlow>
    <!-- For additional details on SpecFlow configuration options see https://github.com/techtalk/SpecFlow/wiki/Configuration -->
    <unitTestProvider name="NUnit" />
  </specFlow>
</configuration>

        [NUnit.Framework.TestAttribute()]
        [NUnit.Framework.DescriptionAttribute("Add two numbers")]
        [NUnit.Framework.CategoryAttribute("mytag")]
        public virtual void AddTwoNumbers()
        {
            TechTalk.SpecFlow.ScenarioInfo scenarioInfo = new TechTalk.SpecFlow.ScenarioInfo("Add two numbers", new string[] {
                        "mytag"});
#line 7
this.ScenarioSetup(scenarioInfo);
#line 8
 testRunner.Given("I have entered 50 into the calculator");
#line 9
 testRunner.And("I have entered 70 into the calculator");
#line 10
 testRunner.When("I press add");
#line 11
 testRunner.Then("the result should be 120 on the screen");
#line hidden
            this.ScenarioCleanup();
        }