fallback to sms template when slack not found

Test Plan:
- Tests pass
- notifications function as normal
- slack notifications still look like sms templated ones

Change-Id: I9025e72fb0085626aa22b586b630bd4cb8b40290
Reviewed-on: https://gerrit.instructure.com/210297
Tested-by: Jenkins
Reviewed-by: Matthew Lemon <mlemon@instructure.com>
QA-Review: Steven Burnett <sburnett@instructure.com>
Product-Review: Steven Burnett <sburnett@instructure.com>

app/models/message.rb

@@ -441,6 +441,7 @@ class Message < ActiveRecord::Base
     path = Canvas::MessageHelper.find_message_path(filename)
 
     if !(File.exist?(path) rescue false)
+      return false if filename.include?('slack')
       filename = self.notification.name.downcase.gsub(/\s/, '_') + ".email.erb"
       path = Canvas::MessageHelper.find_message_path(filename)
     end
@@ -499,8 +500,7 @@ class Message < ActiveRecord::Base
   # Returns message body
   def populate_body(message_body_template, path_type, binding, filename)
     # Build the body content based on the path type
-    self.body = eval(Erubi::Engine.new(message_body_template,
-      bufvar: '@output_buffer').src, binding, filename)
+    self.body = eval(Erubi::Engine.new(message_body_template, bufvar: '@output_buffer').src, binding, filename)
     self.html_body = apply_html_template(binding) if path_type == 'email'
 
     # Append a footer to the body if the path type is email
@@ -545,8 +545,12 @@ class Message < ActiveRecord::Base
     path_type ||= communication_channel.try(:path_type) || 'email'
 
     # Determine the message template file to be used in the message
-    filename = path_type == 'slack' ? template_filename('sms') : template_filename(path_type)
+    filename = template_filename(path_type)
     message_body_template = get_template(filename)
+    if !message_body_template && path_type == 'slack'
+      filename = template_filename('sms')
+      message_body_template = get_template(filename)
+    end
 
     context, asset, user, delayed_messages, data = [self.context,
       self.context, self.user, @delayed_messages, @data]

spec/models/message_spec.rb

@@ -70,6 +70,35 @@ describe Message do
       expect(msg.html_body.index('<!DOCTYPE')).to eq 0
     end
 
+    it "should use slack template if present" do
+      @au = AccountUser.create(:account => account_model)
+      course_with_student
+      alert = @course.alerts.create!(recipients: [:student],
+        criteria: [
+          criterion_type: 'Interaction',
+          threshold: 7
+        ])
+      mock_template = "slack template"
+      expect_any_instance_of(Message).to receive(:get_template).with('alert.slack.erb').and_return(mock_template)
+      msg = generate_message(:alert, :slack, alert)
+      expect(msg.body).to eq mock_template
+    end
+
+    it "should sms template if no slack template present" do
+      @au = AccountUser.create(:account => account_model)
+      course_with_student
+      alert = @course.alerts.create!(recipients: [:student],
+                                      criteria: [
+                                        criterion_type: 'Interaction',
+                                        threshold: 7
+                                      ])
+      mock_template = "sms template"
+      expect_any_instance_of(Message).to receive(:get_template).with('alert.slack.erb').and_return(nil)
+      expect_any_instance_of(Message).to receive(:get_template).with('alert.sms.erb').and_return(mock_template)
+      msg = generate_message(:alert, :slack, alert)
+      expect(msg.body).to eq mock_template
+    end
+
     it "should not html escape the subject" do
       assignment_model(:title => "hey i have weird&<stuff> in my name but that's okay")
       msg = generate_message(:assignment_created, :email, @assignment)