testGetPreviousSibling() {
    setUpDomTree();

    assertNull(
        'No previous sibling', editorNode.getPreviousSibling(gChildTextNode3a));
    assertEquals(
        'Should have text sibling', gChildTextNode3a,
        editorNode.getPreviousSibling(gChildWsNode3));
    assertEquals(
        'Should skip over white space sibling', gChildTextNode3a,
        editorNode.getPreviousSibling(gChildTextNode3b));
    assertNull(
        'No previous sibling', editorNode.getPreviousSibling(gChildMixedNode1));
    assertEquals(
        'Should have mixed text sibling', gChildMixedNode1,
        editorNode.getPreviousSibling(gChildWsNode1));
    assertEquals(
        'Should skip over white space sibling', gChildMixedNode1,
        editorNode.getPreviousSibling(gChildNbspNode1));
    assertNotEquals(
        'Should not move past ws and nbsp', gChildMixedNode1,
        editorNode.getPreviousSibling(gChildTextNode1));
    assertEquals(
        'Should go to child 2', childNode2,
        editorNode.getPreviousSibling(childNode3));
    assertEquals(
        'Should go to child 1', childNode1,
        editorNode.getPreviousSibling(childNode2));
    assertNull(
        'Only has white space siblings',
        editorNode.getPreviousSibling(gChildWsNode2b));

    tearDownDomTree();
  }
Creates a DOM tree and Test that getPreviousSibling properly ignores
ignorable nodes