fix 500 level errors in discussion helpers

fixes VICE-1426
fixes VICE-1427

flag=none

test plan:
- specs, old and new, pass

it seems like this is only a helper
method for when quickly writing specs
and stuff. so risk is very low

Change-Id: I4fe474ade6b1acfba0074135489add4d0bf464c6
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/264850
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Rob Orton <rob@instructure.com>
QA-Review: Rob Orton <rob@instructure.com>
Product-Review: Rob Orton <rob@instructure.com>

app/models/discussion_entry.rb

@@ -170,9 +170,9 @@ class DiscussionEntry < ActiveRecord::Base
     end
     user = nil unless user && self.context.users.include?(user)
     if !user
-      raise "Only context participants may reply to messages"
+      raise IncomingMail::Errors::InvalidParticipant
     elsif !message || message.empty?
-      raise "Message body cannot be blank"
+      raise IncomingMail::Errors::BlankMessage
     else
       self.shard.activate do
         entry = discussion_topic.discussion_entries.new(message: message,

app/models/discussion_topic.rb

@@ -1044,9 +1044,9 @@ class DiscussionTopic < ActiveRecord::Base
     end
     user = nil unless user && self.context.users.include?(user)
     if !user
-      raise "Only context participants may reply to messages"
+      raise IncomingMail::Errors::InvalidParticipant
     elsif !message || message.empty?
-      raise "Message body cannot be blank"
+      raise IncomingMail::Errors::BlankMessage
     elsif !self.grants_right?(user, :read)
       nil
     else

app/models/incoming_mail/errors.rb

@@ -24,5 +24,7 @@ module IncomingMail
     class UnknownSender < ReplyFrom; end
     class ReplyToLockedTopic < ReplyFrom; end
     class ReplyToDeletedDiscussion < ReplyFrom; end
+    class InvalidParticipant < ReplyFrom; end
+    class BlankMessage < ReplyFrom; end
   end
 end

spec/models/discussion_entry_spec.rb

@@ -640,6 +640,15 @@ describe DiscussionEntry do
       student_in_course(:course => @course)
       expect { @entry.reply_from(:user => @student, :text => "reply") }.to raise_error(IncomingMail::Errors::ReplyToLockedTopic)
     end
+
+    it 'raises InvalidParticipant for invalid participants' do
+      u = user_with_pseudonym(:active_user => true, :username => 'test1@example.com', :password => 'test1234')
+      expect { @topic.reply_from(user: u, text: "entry 1") }.to raise_error IncomingMail::Errors::InvalidParticipant
+    end
+
+    it 'raises BlankMessage for blank message' do
+      expect { @topic.reply_from(user: @teacher, text: '') }.to raise_error IncomingMail::Errors::BlankMessage
+    end
   end
 
   context 'stream items' do

spec/models/discussion_topic_spec.rb

@@ -2515,6 +2515,26 @@ describe DiscussionTopic do
     end
   end
 
+  describe 'reply_from' do
+    before(:once) do
+      @topic = @course.discussion_topics.create!(user: @teacher, message: 'topic')
+    end
+
+    it 'returns entry for valid arguments' do
+      val = @topic.reply_from(:user => @teacher, :text => "entry 1")
+      expect(val).to be_a_kind_of DiscussionEntry
+    end
+
+    it 'raises InvalidParticipant for invalid participants' do
+      u = user_with_pseudonym(:active_user => true, :username => 'test1@example.com', :password => 'test1234')
+      expect { @topic.reply_from(user: u, text: "entry 1") }.to raise_error IncomingMail::Errors::InvalidParticipant
+    end
+
+    it 'raises BlankMessage for empty message' do
+      expect { @topic.reply_from(user: @teacher, text: '') }.to raise_error IncomingMail::Errors::BlankMessage
+    end
+  end
+
   describe 'to_podcast' do
     it "includes media extension in enclosure url even though it is a redirect (for itunes)" do
       @topic = @course.discussion_topics.create!(