Use #tap to distinguish Duration from UnknownDuration

lib/cucumber/core/test/result.rb

@@ -195,20 +195,20 @@ def increment_total(status)
         end
 
         class Duration
-          attr_reader :duration
+          attr_reader :nanoseconds
 
-          def initialize(duration)
-            @duration = duration
+          def initialize(nanoseconds)
+            @nanoseconds = nanoseconds
           end
         end
 
         class UnknownDuration
-          def nil?
-            true
+          def tap(&block)
+            self
           end
 
-          def duration
-            0
+          def nanoseconds
+            raise "#nanoseconds only allowed to be used in #tap block"
           end
         end
       end

spec/cucumber/core/test/duration_matcher.rb

@@ -5,13 +5,15 @@
 module Cucumber::Core::Test
   RSpec::Matchers.define :be_duration do |expected|
     match do |actual|
-      not actual.nil? and actual.duration == expected
+      actual.tap { |duration| @nanoseconds = duration.nanoseconds }
+      @nanoseconds == expected
     end
   end
 
   RSpec::Matchers.define :an_unknown_duration do
     match do |actual|
-      actual.nil? and expect(actual).to respond_to(:duration)
+      actual.tap { raise "#tap block was executed, not an UnknownDuration" } 
+      expect(actual).to respond_to(:nanoseconds)
     end
   end
 end

spec/cucumber/core/test/result_spec.rb

@@ -191,24 +191,21 @@ def describe_to(visitor, *args)
     describe Result::Duration do
       subject(:duration) { Result::Duration.new(10) }
 
-      it "nil? returns false" do
-        expect( duration.nil? ).to be_falsy
-      end
-
-      it "has a duration" do
-        expect( duration.duration ).to eq 10
+      it "#nanoseconds can be accessed in #tap" do
+        expect( duration.tap { |duration| @duration = duration.nanoseconds } ).to eq duration
+        expect( @duration ).to eq 10
       end
     end
 
     describe Result::UnknownDuration do
       subject(:duration) { Result::UnknownDuration.new }
 
-      it "nil? returns true" do
-        expect( duration.nil? ).to be_truthy
+      it "#tap does not execute the passed block" do
+        expect( duration.tap { raise "tap executed block" } ).to eq duration
       end
 
-      it "return duration 0" do
-        expect( duration.duration ).to eq 0
+      it "accessing #nanoseconds outside #tap block raises exception" do
+        expect { duration.nanoseconds }.to raise_error(RuntimeError)
       end
     end
   end