Fix issue 5

lib/jsonapi_spec_helpers.rb

@@ -3,6 +3,7 @@
 require 'jsonapi_spec_helpers/helpers'
 require 'jsonapi_spec_helpers/payload'
 require 'jsonapi_spec_helpers/payload_sanitizer'
+require 'jsonapi_spec_helpers/errors'
 
 module JsonapiSpecHelpers
   def self.included(klass)

lib/jsonapi_spec_helpers/errors.rb

@@ -0,0 +1,16 @@
+module JsonapiSpecHelpers
+  module Errors
+    class Base < StandardError; end
+    class IncludedOutOfBounds < Base
+      def initialize(type, index, array)
+        @type = type; @index = index; @array = array
+      end
+
+      def message
+        "You attempted to get an item at index #{@index} of the type '#{@type}' " \
+        "from the included property of your JSON payload. But it contained "    \
+        "#{@array.length} '#{@type}'"
+      end
+    end
+  end
+end

lib/jsonapi_spec_helpers/helpers.rb

@@ -39,7 +39,11 @@ def json_includes(type, *indices)
       indices  = (0...included.length).to_a if indices.empty?
       includes = []
       indices.each do |index|
-        includes << json_item(from: included.at(index))
+        single_included = included.at(index)
+        if single_included.nil?
+          raise Errors::IncludedOutOfBounds.new(type, index, included)
+        end
+        includes << json_item(from: single_included)
       end
       includes
     end

spec/helpers_spec.rb

@@ -173,6 +173,10 @@
       it 'is only includes of a given type at indices' do
         expect(json_includes('comments', 1).length).to eq(1)
       end
+
+      it 'throws when asking for an index beyond the length of the includes' do
+        expect{ json_includes('comments', 99) }.to raise_error JsonapiSpecHelpers::Errors::IncludedOutOfBounds
+      end
     end
   end