Extract tracker into supervision tree.

test/tracker_test.exs

@@ -4,25 +4,25 @@ defmodule TrackerTest do
   @sample_modules [SampleKoan, PassingKoan]
 
   test "can start" do
-    Tracker.start(@sample_modules)
+    Tracker.set_total(@sample_modules)
     assert Tracker.summarize == %{total: 2, current: 0, visited_modules: []}
   end
 
   test "can be notified of completed koans" do
-    Tracker.start(@sample_modules)
+    Tracker.set_total(@sample_modules)
     Tracker.completed(SampleKoan, :"Hi there")
     assert Tracker.summarize == %{total: 2, current: 1, visited_modules: [SampleKoan]}
   end
 
   test "multiple comletions of the same koan count only once" do
-    Tracker.start(@sample_modules)
+    Tracker.set_total(@sample_modules)
     Tracker.completed(SampleKoan, :"Hi there")
     Tracker.completed(SampleKoan, :"Hi there")
     assert Tracker.summarize == %{total: 2, current: 1, visited_modules: [SampleKoan]}
   end
 
   test "knows when koans are not complete" do
-    Tracker.start(@sample_modules)
+    Tracker.set_total(@sample_modules)
     refute Tracker.complete?
   end
 end