public @NotNull PsiElement createComma() {
    final YAMLFile file = createDummyYamlWithText("[1,2]");
    final PsiElement comma = file.findElementAt("[1".length());
    assert comma != null && comma.getNode().getElementType() == YAMLTokenTypes.COMMA;
    return comma;
  }
public @NotNull PsiElement createComma()