My panda level - add average grade feature

.gitignore

@@ -0,0 +1 @@
+.rspec

Gemfile.lock

@@ -10,6 +10,8 @@ GEM
     diff-lcs (1.1.3)
     gherkin (2.10.0)
       json (>= 1.4.6)
+    gherkin (2.10.0-x86-mingw32)
+      json (>= 1.4.6)
     json (1.7.3)
     rack (1.4.1)
     rspec (2.10.0)
@@ -23,6 +25,7 @@ GEM
 
 PLATFORMS
   ruby
+  x86-mingw32
 
 DEPENDENCIES
   cucumber

features/step_definitions/teacher_average_grade_steps.rb

@@ -0,0 +1,22 @@
+Given /^I have multiple students$/ do
+  @teacher  = Teacher.new
+  @student1 = Student.new
+  @student2 = Student.new
+  @student3 = Student.new
+end
+
+Given /^each one has submitted an assignment$/ do
+  @teacher.submit_assignment(@student1, Assignment.new)
+  @teacher.submit_assignment(@student2, Assignment.new)
+  @teacher.submit_assignment(@student3, Assignment.new)
+end
+
+When /^I give the assignments a grade$/ do
+  @teacher.record_grade(@student1, 95)
+  @teacher.record_grade(@student2, 50)
+  @teacher.record_grade(@student3, 80)
+end
+
+Then /^I can view the average grade for my class$/ do
+  @teacher.average_grade(@teacher.assignments).should eq(75)
+end

features/teacher_can_view_average_grade.feature

@@ -0,0 +1,11 @@
+Feature: Teacher can view average grade for the class
+
+  As a Teacher
+  I can view the average grade for my class
+  So I can establish a grading curve
+
+  Scenario: Teacher can view average grade for the class
+    Given I have multiple students
+    And each one has submitted an assignment
+    When I give the assignments a grade
+    Then I can view the average grade for my class

lib/teacher.rb

@@ -1,4 +1,6 @@
 class Teacher
+  attr_reader :assignments
+
   def initialize
     @assignments = {}
   end
@@ -9,6 +11,12 @@ def record_grade(student, grade)
     @assignments[student] = assignment
   end
 
+  def average_grade(assignments)
+    class_grades = assignments.map { |student, assignment| assignment.grade }
+    sum_of_class_grades = class_grades.inject(:+)
+    sum_of_class_grades / assignments.size
+  end
+
   def submit_assignment(student, assignment)
     @assignments[student] = assignment
   end

spec/teacher_spec.rb

@@ -3,20 +3,31 @@
 
 describe Teacher do
   it "should store assignments" do
-    student = stub
-    assignment = stub
+    student = double
+    assignment = double
     subject.submit_assignment(student, assignment)
     subject.assignment_for_student(student).should eq(assignment)
   end
 
 
   describe "should record a grade" do
     it "should record the grade" do
-      student = stub
-      assignment = mock
+      student = double
+      assignment = double
       assignment.should_receive(:grade=).with(95)
       subject.submit_assignment(student, assignment)
       subject.record_grade(student, 95)
     end
   end
+
+  describe "should provide an average grade for the class" do
+    it "should provide an average grade" do
+      assignment_doubles = {
+                            student1: double("Assignment", grade: 95),
+                            student2: double("Assignment", grade: 50),
+                            student3: double("Assignment", grade: 80)
+                            }
+    subject.average_grade(assignment_doubles).should eq(75)
+    end
+  end
 end