make qunit test order shuffling reproducible

shuffle the tests in the rake task instead of the runner.
 * the specific order used in a test run is preserved in
   spec/javascripts/tests.js, so it's easy to tell which tests
   ran before the failing one.
 * the PRNG seed is displayed in the log output, and can be
   re-used via the `seed` environment variable, making test
   failures dependent on run order much easier to reproduce.

refs CNVS-20850

Change-Id: I2538789d8b4102976e456ab4b89924bde0c5b709
Reviewed-on: https://gerrit.instructure.com/55530
Tested-by: Jenkins
Reviewed-by: Simon Williams <simon@instructure.com>
Reviewed-by: Ethan Vizitei <evizitei@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>
QA-Review: Jeremy Stanley <jeremy@instructure.com>

lib/tasks/js.rake

@@ -38,6 +38,17 @@ namespace :js do
     build_requirejs_config
   end
 
+  def generate_prng
+    if ENV["seed"]
+      seed = ENV["seed"].to_i
+    else
+      srand
+      seed = rand(1 << 20)
+    end
+    puts "--> randomized with seed #{seed}"
+    Random.new(seed)
+  end
+
   def build_requirejs_config
     require 'canvas/require_js'
     require 'erubis'
@@ -52,7 +63,7 @@ namespace :js do
       "spec/plugins/*/javascripts/compiled/#{matcher}"
     ].map{ |file| file.sub(/\.js$/, '').sub(/public\/javascripts\//, '') }
     File.open("#{Rails.root}/spec/javascripts/tests.js", 'w') { |f|
-      f.write("window.__TESTS__ = #{JSON.pretty_generate(tests)}")
+      f.write("window.__TESTS__ = #{JSON.pretty_generate(tests.shuffle(random: generate_prng))}")
     }
   end
 
@@ -85,7 +96,7 @@ namespace :js do
   end
 
   def test_suite(reporter=nil)
-    if test_js_with_timeout(300,reporter) != 0 && !ENV['JS_SPEC_MATCHER']
+    if test_js_with_timeout(300,reporter) != 0 && !ENV['JS_SPEC_MATCHER'] && ENV['retry'] != 'false'
       puts "--> Karma tests failed." # retrying karma...
       raise "Karma tests failed on second attempt." if test_js_with_timeout(400,reporter) != 0
     end

spec/javascripts/load_tests.js

@@ -1,5 +1,4 @@
-tests = shuffle(__TESTS__);
+tests = __TESTS__;
-// tests = __TESTS__
 // tests = tests.slice(0,50);
 // console.log(tests);
 
@@ -40,16 +39,3 @@ if(window.__karma__) {
     }
   });
 }
-
-// Fisher-Yates shuffle
-// http://jsperf.com/fisher-yates-compare-shuffle/12
-function shuffle(array) {
-  var tmp, current, top = array.length;
-  if (top) while (top) {
-    current = (Math.random() * (top--)) | 0;
-    tmp = array[current];
-    array[current] = array[top];
-    array[top] = tmp;
-  }
-  return array;
-}