```ruby
require File.expand_path('../../../spec_helper', __FILE__)

with_feature :fiber do
  describe "Fiber.new" do
    it "creates a fiber from the given block" do
      fiber = Fiber.new {}
      fiber.should be_an_instance_of(Fiber)
    end

    it "raises an ArgumentError if called without a block" do
      lambda { Fiber.new }.should raise_error(ArgumentError)
    end

    it "does not invoke the block" do
      invoked = false
      fiber = Fiber.new { invoked = true }
      invoked.should be_false
    end

    it "closes over lexical environments" do
      o = Object.new
      def o.f
        a = 1
        f = Fiber.new { a = 2 }
        f.resume
        a
      end
      o.f.should == 2
    end

    it "escapes an inner ensure block" do
      f = Fiber.new do
        begin
          :begin
        rescue
          :rescue
        ensure
          :ensure
        end
      end
      f.resume.should == :begin
    end

    it "raises a SyntaxError when the block contains a retry statement" do
      lambda { eval 'Fiber.new { retry; }' }.should raise_error(SyntaxError)
    end
  end
end
```

Remove Fiber + ensure spec that doesn't actually test anything.
user
```ruby
require File.expand_path('../../../spec_helper', __FILE__)

with_feature :fiber do
  describe "Fiber.new" do
    it "creates a fiber from the given block" do
      fiber = Fiber.new {}
      fiber.should be_an_instance_of(Fiber)
    end

    it "raises an ArgumentError if called without a block" do
      lambda { Fiber.new }.should raise_error(ArgumentError)
    end

    it "does not invoke the block" do
      invoked = false
      fiber = Fiber.new { invoked = true }
      invoked.should be_false
    end

    it "closes over lexical environments" do
      o = Object.new
      def o.f
        a = 1
        f = Fiber.new { a = 2 }
        f.resume
        a
      end
      o.f.should == 2
    end

    it "raises a SyntaxError when the block contains a retry statement" do
      lambda { eval 'Fiber.new { retry; }' }.should raise_error(SyntaxError)
    end
  end
end
```
assistant