[added] includeSrcNode takes "asString" as option.

"asString" pushes the violating srcNode.outerHTML to the warning
message so it gives a better description when using react-a11y in
ci. Keeps existing functionality with `includeSrcNode: true`

Signed-off-by: Matt Royal <mroyal@pivotal.io>
Signed-off-by: Geoff Pleiss <gpleiss@pivotal.io>

Author: Kenny Wang

lib/__tests__/index-test.js

@@ -8,7 +8,9 @@ var k = () => {};
 var captureWarnings = (fn) => {
   var _warn = console.warn;
   var msgs = {};
-  console.warn = (id, msg) => msgs[msg] = true;
+  console.warn = (id, msg, srcNode) => {
+    msgs[msg] = srcNode ? srcNode : true;
+  };
   fn();
   console.warn = _warn;
   return msgs;
@@ -557,6 +559,45 @@ describe('labels', () => {
   });
 });
 
+describe('includeSrcNode is "asString"', () => {
+  var createElement = React.createElement;
+  var fixture;
+
+  before(() => {
+    a11y(React, { includeSrcNode: "asString" });
+    fixture = document.createElement('div');
+    fixture.id = 'fixture-1';
+    document.body.appendChild(fixture);
+  });
+
+  after(() => {
+    React.createElement = createElement;
+    fixture = document.getElementById('fixture-1');
+    if (fixture)
+      document.body.removeChild(fixture);
+  });
+
+  it('returns the outerHTML as a string in the error message', () => {
+    var Bar = React.createClass({
+      _privateProp: 'bar',
+
+      componentDidMount: function() {
+        return this._privateProp;
+      },
+      render: () => {
+        return (
+          <div role="button"></div>
+        );
+      }
+    });
+
+    var msgs = captureWarnings(() => {React.render(<Bar/>, fixture);});
+    var regex = /^Source Node: <(\w+) .+>.*<\/\1>/;
+    var matches = msgs[assertions.render.NO_LABEL.msg].match(regex);
+    assert.equal(matches[1], "div");
+  });
+});
+
 describe('filterFn', () => {
   var createElement = React.createElement;
 

lib/index.js

@@ -110,10 +110,11 @@ var logWarning = (component, failureInfo, options) => {
       // Guard against logging null element references should render()
       // return null or false.
       // https://facebook.github.io/react/docs/component-api.html#getdomnode
-      if (srcNode)
+      if (includeSrcNode === "asString")
+        warning.push("Source Node: " + srcNode.outerHTML);
+      else if (srcNode)
         warning.push(srcNode);
     }
-
     console.warn.apply(console, warning);
   };
 
@@ -127,7 +128,7 @@ var logWarning = (component, failureInfo, options) => {
 };
 
 var handleFailure = (options, reactEl, type, props, failureMsg) => {
-  var includeSrcNode = options && !!options.includeSrcNode;
+  var includeSrcNode = options && (options.includeSrcNode || false);
   var warningPrefix = (options && options.warningPrefix) || '';
   var reactComponent = reactEl._owner;