set up grading_period model, migration, and tests

closes CNVS-15906

test plan:
-run rake db:migrate
-verify the migration successfully runs, creating the grading_periods table and adding the index for course_id and account_id

Change-Id: If991a00fc79bc4aecabe8189a43432e2158709c8
Reviewed-on: https://gerrit.instructure.com/42161
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jacob Fugal <jacob@instructure.com>
Reviewed-by: Josh Simpson <jsimpson@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>
Product-Review: Spencer Olson <solson@instructure.com>

app/models/grading_period.rb

@@ -0,0 +1,15 @@
+class GradingPeriod < ActiveRecord::Base
+  attr_accessible :course, :account, :weight, :start_date, :end_date
+
+  belongs_to :course
+  belongs_to :account
+
+  validates_presence_of :weight, :start_date, :end_date
+  validate :validate_dates
+
+  def validate_dates
+    if self.start_date && self.end_date
+      errors.add(:end_date, t('errors.invalid_grading_period_end_date', "Grading period end date precedes start date")) if self.end_date < self.start_date
+    end
+  end
+end

db/migrate/20141001211428_create_grading_periods.rb

@@ -0,0 +1,21 @@
+class CreateGradingPeriods < ActiveRecord::Migration
+  tag :predeploy
+
+  def self.up
+    create_table :grading_periods do |t|
+      t.integer :course_id, :limit => 8
+      t.integer :account_id, :limit => 8
+      t.float :weight, :null => false
+      t.datetime :start_date, :null => false
+      t.datetime :end_date, :null => false
+      t.timestamps
+    end
+
+    add_index :grading_periods, :course_id
+    add_index :grading_periods, :account_id
+  end
+
+  def self.down
+    drop_table :grading_periods
+  end
+end

spec/models/grading_period_spec.rb

@@ -0,0 +1,103 @@
+#
+# Copyright (C) 2014 Instructure, Inc.
+#
+# This file is part of Canvas.
+#
+# Canvas is free software: you can redistribute it and/or modify it under
+# the terms of the GNU Affero General Public License as published by the Free
+# Software Foundation, version 3 of the License.
+#
+# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
+# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
+# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along
+# with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+
+require File.expand_path(File.dirname(__FILE__) + '/../spec_helper.rb')
+
+describe GradingPeriod do
+  before (:all) do
+    @grading_period = GradingPeriod.create(course_id: 1, weight: 25.0, start_date: Time.zone.now, end_date: 1.day.from_now)
+  end
+
+  it "should respond to course_id" do
+    expect(@grading_period).to respond_to(:course_id)
+  end
+
+  it "should respond to account_id" do
+    expect(@grading_period).to respond_to(:account_id)
+  end
+
+  it "should respond to weight" do
+    expect(@grading_period).to respond_to(:weight)
+  end
+
+  it "should respond to start_date" do
+    expect(@grading_period).to respond_to(:start_date)
+  end
+
+  it "should respond to end_date" do
+    expect(@grading_period).to respond_to(:end_date)
+  end
+
+  it "should respond to course" do
+    expect(@grading_period).to respond_to(:course)
+  end
+
+  it "should respond to account" do
+    expect(@grading_period).to respond_to(:account)
+  end
+
+  context "associations" do
+    it "should belong to a course" do
+      association = GradingPeriod.reflect_on_association(:course)
+      association.macro.should == :belongs_to
+    end
+
+    it "should belong to an account" do
+      association = GradingPeriod.reflect_on_association(:account)
+      association.macro.should == :belongs_to
+    end
+  end
+
+  context "validation" do
+    it "should be valid with appropriate input" do
+      expect(@grading_period).to be_valid
+    end
+
+    it "should require a weight" do
+      expect(GradingPeriod.create(course_id: 1, start_date: Time.zone.now, end_date: 1.day.from_now )).to_not be_valid
+    end
+
+    it "should require a start_date" do
+      expect(GradingPeriod.create(course_id: 1, weight: 25.0, end_date: 1.day.from_now)).to_not be_valid
+    end
+
+    it "should require an end_date" do
+      expect(GradingPeriod.create(course_id: 1, weight: 25.0, start_date: Time.zone.now)).to_not be_valid
+    end
+
+    context "when end_date is before the start_date" do
+      it "should not be able to create a grading period with end_date before the start_date" do
+        expect(GradingPeriod.create(course_id: 1, weight: 25.0, start_date: 2.days.from_now, end_date: Time.zone.now)).to_not be_valid
+      end
+
+      it "should not be able to update the end_date to be before the start_date" do
+        grading_period = GradingPeriod.create(course_id: 1, weight: 25.0, start_date: Time.zone.now, end_date: 1.day.from_now)
+        expect(grading_period).to be_valid
+        grading_period.update_attributes(end_date: 1.day.ago)
+        expect(grading_period).not_to be_valid
+      end
+
+      it "should not be able to update the start_date to be after the end_date" do
+        grading_period = GradingPeriod.create(course_id: 1, weight: 25.0, start_date: Time.zone.now, end_date: 1.day.from_now)
+        expect(grading_period).to be_valid
+        grading_period.update_attributes(start_date: 2.days.from_now)
+        expect(grading_period).not_to be_valid
+      end
+    end
+  end
+end