feat: make editable code available in tests

client/src/templates/Challenges/utils/build.js

@@ -53,13 +53,15 @@ function buildSourceMap(files) {
   // the same name 'index'. This made the last file the only file to  appear in
   // sources.
   // A better solution is to store and handle them separately. Perhaps never
-  // setting the name to 'index'.
+  // setting the name to 'index'. Use 'contents' instead?
+  // TODO: is file.source ever defined?
   return files.reduce(
     (sources, file) => {
       sources[file.name] += file.source || file.contents;
+      sources.editableContents += file.editableContents;
       return sources;
     },
-    { index: '' }
+    { index: '', editableContents: '' }
   );
 }
 
@@ -111,7 +113,10 @@ export function getTestRunner(buildData, { proxyLogger }, document) {
 }
 
 function getJSTestRunner({ build, sources }, proxyLogger) {
-  const code = sources && 'index' in sources ? sources['index'] : '';
+  const code = {
+    contents: sources.index,
+    editableContents: sources.editableContents
+  };
 
   const testWorker = createWorker(testEvaluator, { terminateWorker: true });