**Do you want to request a _feature_ or report a _bug_?**

Report a bug.

**What is the current behavior?**

When testing components, `Warning: ReactComponentTreeDevtool: Missing React element for debugID 1 when building stack` is shown when calling `TestUtils.renderIntoDocument`.

**If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem via https://jsfiddle.net or similar (template: https://jsfiddle.net/reactjs/69z2wepo/).**

https://github.com/angusfretwell/reproduce-debugid-warning (`npm install && npm test`).

**What is the expected behavior?**

According to #7187 this is an internal warning and shouldn't be displayed.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**
- react@15.2.1
- react-addons-test-utils@15.2.1
- react-dom@15.2.1

I didn't receive this warning on 15.2.0.

}
    }
    return originalKeys;
  },
  /**
   * Retrieves the rendered children in a nice format for comparing to the input
   * `this.props.usernameToStatus`.
   */
  getStatusDisplays: function() {
    var res = {};
    var i;
    var originalKeys = this.getOriginalKeys();
    for (i = 0; i < originalKeys.length; i++) {
      var key = originalKeys[i];
      res[key] = this.refs[key];
    }
    return res;
  },
  /**
   * Verifies that by the time a child is flushed, the refs that appeared
   * earlier have already been resolved.
   * TODO: This assumption will likely break with incremental reconciler
   * but our internal layer API depends on this assumption. We need to change
   * it to be more declarative before making ref resolution indeterministic.
   */
  verifyPreviousRefsResolved: function(flushedKey) {
    var i;
    var originalKeys = this.getOriginalKeys();
    for (i = 0; i < originalKeys.length; i++) {
      var key = originalKeys[i];