Tests that expanding elements recursively works.

===== Initial state of tree outline =====

+ <div id="depth-1">…</div>

===== State of tree outline after calling .expandRecursively() =====

- <div id="depth-1">
    - <div id="depth-2">
        - <div id="depth-3">
            - <div id="depth-4">
                - <div id="depth-5">
                    - <div id="depth-6">
                        - <div id="depth-7">
                            - <div id="depth-8">
                                - <div id="depth-9">
                                      <div id="depth-10"></div>
                                  </div>
                              </div>
                          </div>
                      </div>
                  </div>
              </div>
          </div>
      </div>
  </div>