remove test_data and rely on data passed from rails

app/assets/javascripts/burndown_chart/index.js

 import Cookies from 'js-cookie';
 import BurndownChart from './burndown_chart';
-import testData from './test_data.json';
 
 $(() => {
   // handle hint dismissal
@@ -10,14 +9,20 @@ $(() => {
     Cookies.set('hide_burndown_message', 'true');
   });
 
-  // render chart
-  const chart = new BurndownChart({
-    container: '.burndown-chart',
-    startDate: '2017-03-01',
-    dueDate: '2017-03-31',
-  });
+  // generate burndown chart (if data available)
+  const container = '.burndown-chart';
+  const chartElm = $(container);
+
+  if (chartElm.length) {
+    const startDate = chartElm.data('startDate');
+    const dueDate = chartElm.data('endDate');
+    const chartData = chartElm.data('chartData');
+
+    const chart = new BurndownChart({ container, startDate, dueDate });
+
+    chart.setData(chartData, { label: 'Open Issues', animate: true });
 
-  chart.setData(testData, { label: 'Open Issues', animate: true });
-  window.addEventListener('resize', () => chart.animateResize(1));
-  $(document).on('click', '.js-sidebar-toggle', () => chart.animateResize(2));
+    window.addEventListener('resize', () => chart.animateResize(1));
+    $(document).on('click', '.js-sidebar-toggle', () => chart.animateResize(2));
+  }
 });

app/assets/javascripts/burndown_chart/test_data.json

-[
-  ["2017-03-01", "54"],
-  ["2017-03-02", "52"],
-  ["2017-03-03", "51"],
-  ["2017-03-04", "47"],
-  ["2017-03-05", "48"],
-  ["2017-03-06", "44"],
-  ["2017-03-07", "41"],
-  ["2017-03-08", "35"],
-  ["2017-03-09", "32"],
-  ["2017-03-10", "32"],
-  ["2017-03-11", "31"],
-  ["2017-03-12", "29"],
-  ["2017-03-13", "26"],
-  ["2017-03-14", "23"],
-  ["2017-03-15", "20"]
-]

app/views/projects/milestones/show.html.haml

@@ -49,7 +49,7 @@
             = preserve do
               = markdown_field(@milestone, :description)
 
-  = render 'shared/milestones/burndown', milestone: @milestone, project: @project
+  = render 'shared/milestones/burndown', milestone: @milestone, project: @project, burndown: @burndown
 
   - if can?(current_user, :read_issue, @project) && @milestone.total_items_count(current_user).zero?
     .alert.alert-success.prepend-top-default

app/views/shared/milestones/_burndown.html.haml

 - milestone = local_assigns[:milestone]
 - project = local_assigns[:project]
-- can_generate_chart = @milestone.start_date && @milestone.due_date
+- burndown = local_assigns[:burndown]
+- can_generate_chart = burndown.start_date && burndown.end_date && burndown
 
 - content_for :page_specific_javascripts do
   = page_specific_javascript_bundle_tag('common_d3')
@@ -25,4 +26,4 @@
   .burndown-header
     %h3
       Open issues
-  .burndown-chart
+  .burndown-chart{ data: { start_date: burndown.start_date.strftime("%Y-%m-%d"), end_date: burndown.end_date.strftime("%Y-%m-%d"), chart_data: burndown.chart_data.to_json } }