AnotherSpec.cs

[Tag("AnotherTag")]
class AnotherSpec : nspec
{
    void describe_rentabilidade_produtos()
    {
      context["when data are valids"] = () =>
      {
          it["b"].should_be("b");
      }
 
    }
}

SomeSpec.cs

[Tag("SomeTag")]
class SomeSpec : nspec
{
 
    void before_all()
    {
        Console.WriteLine("Database stuff...");
    }
    
    void describe_rentabilidade_produtos()
    {
      context["when data are valids"] = () =>
      {
          it["test"].should_be("test");
      }
 
    }
}

Here is how i'm running tests:

NSpecRunner.exe Everest.ControleFundos.Specs.dll --tag SomeTag;
NSpecRunner.exe Everest.ControleFundos.Specs.dll --tag AnotherTag;