Show testrun results in statistics

app/models/code_ocean/file.rb

@@ -21,6 +21,7 @@ module CodeOcean
     belongs_to :file_type
 
     has_many :files
+    has_many :testruns
     alias_method :descendants, :files
 
     mount_uploader :native_file, FileUploader

app/models/submission.rb

@@ -7,6 +7,8 @@ class Submission < ActiveRecord::Base
 
   belongs_to :exercise
 
+  has_many :testruns
+
   delegate :execution_environment, to: :exercise
 
   scope :final, -> { where(cause: 'submit') }