def test_invalid_url_error(urlutils_message_mock, url, valid, has_err_string):
    """Test invalid_url_error().

    Args:
        url: The URL to check.
        valid: Whether the QUrl is valid (isValid() == True).
        has_err_string: Whether the QUrl is expected to have errorString set.
    """
    qurl = QUrl(url)
    assert qurl.isValid() == valid
    if valid:
        with pytest.raises(ValueError):
            urlutils.invalid_url_error(0, qurl, '')
        assert not urlutils_message_mock.messages
    else:
        assert bool(qurl.errorString()) == has_err_string
        urlutils.invalid_url_error(0, qurl, 'frozzle')

        msg = urlutils_message_mock.getmsg(urlutils_message_mock.Level.error)
        if has_err_string:
            expected_text = ("Trying to frozzle with invalid URL - " +
                             qurl.errorString())
        else:
            expected_text = "Trying to frozzle with invalid URL"
        assert msg.text == expected_text

    def get(self, url, page=None, fileobj=None, filename=None,
            auto_remove=False):
        """Start a download with a link URL.

        Args:
            url: The URL to get, as QUrl
            page: The QWebPage to get the download from.
            fileobj: The file object to write the answer to.
            filename: A path to write the data to.
            auto_remove: Whether to remove the download even if
                         ui -> remove-finished-downloads is set to false.

        Return:
            If the download could start immediately, (fileobj/filename given),
            the created DownloadItem.

            If not, None.
        """
        if fileobj is not None and filename is not None:
            raise TypeError("Only one of fileobj/filename may be given!")
        if not url.isValid():
            urlutils.invalid_url_error(self._win_id, url, "start download")
            return
        req = QNetworkRequest(url)
        return self.get_request(req, page, fileobj, filename, auto_remove)

    def _remove_tab(self, tab):
        """Remove a tab from the tab list and delete it properly.

        Args:
            tab: The QWebView to be closed.
        """
        idx = self.indexOf(tab)
        if idx == -1:
            raise ValueError("tab {} is not contained in TabbedWidget!".format(
                tab))
        if tab is self._now_focused:
            self._now_focused = None
        if tab is objreg.get('last-focused-tab', None, scope='window',
                             window=self._win_id):
            objreg.delete('last-focused-tab', scope='window',
                          window=self._win_id)
        if tab.cur_url.isValid():
            history_data = qtutils.serialize(tab.history())
            entry = UndoEntry(tab.cur_url, history_data)
            self._undo_stack.append(entry)
        elif tab.cur_url.isEmpty():
            # There are some good reasons why an URL could be empty
            # (target="_blank" with a download, see [1]), so we silently ignore
            # this.
            # [1] https://github.com/The-Compiler/qutebrowser/issues/163
            pass
        else:
            # We display a warnings for URLs which are not empty but invalid -
            # but we don't return here because we want the tab to close either
            # way.
            urlutils.invalid_url_error(self._win_id, tab.cur_url, "saving tab")
        tab.shutdown()
        self.removeTab(idx)
        tab.deleteLater()

    def _remove_tab(self, tab, *, add_undo=True, new_undo=True, crashed=False):
        """Remove a tab from the tab list and delete it properly.

        Args:
            tab: The QWebView to be closed.
            add_undo: Whether the tab close can be undone.
            new_undo: Whether the undo entry should be a new item in the stack.
            crashed: Whether we're closing a tab with crashed renderer process.
        """
        idx = self.widget.indexOf(tab)
        if idx == -1:
            if crashed:
                return
            raise TabDeletedError("tab {} is not contained in "
                                  "TabbedWidget!".format(tab))
        if tab is self._now_focused:
            self._now_focused = None
        if tab is objreg.get('last-focused-tab', None, scope='window',
                             window=self._win_id):
            objreg.delete('last-focused-tab', scope='window',
                          window=self._win_id)

        if tab.url().isEmpty():
            # There are some good reasons why a URL could be empty
            # (target="_blank" with a download, see [1]), so we silently ignore
            # this.
            # [1] https://github.com/qutebrowser/qutebrowser/issues/163
            pass
        elif not tab.url().isValid():
            # We display a warning for URLs which are not empty but invalid -
            # but we don't return here because we want the tab to close either
            # way.
            urlutils.invalid_url_error(tab.url(), "saving tab")
        elif add_undo:
            try:
                history_data = tab.history.serialize()
            except browsertab.WebTabError:
                pass  # special URL
            else:
                entry = UndoEntry(tab.url(), history_data, idx,
                                  tab.data.pinned)
                if new_undo or not self._undo_stack:
                    self._undo_stack.append([entry])
                else:
                    self._undo_stack[-1].append(entry)

        tab.shutdown()
        self.widget.removeTab(idx)
        if not crashed:
            # WORKAROUND for a segfault when we delete the crashed tab.
            # see https://bugreports.qt.io/browse/QTBUG-58698
            tab.layout().unwrap()
            tab.deleteLater()

    def get(self, url, page):
        """Start a download with a link URL.

        Args:
            url: The URL to get, as QUrl
            page: The QWebPage to get the download from.
        """
        if not url.isValid():
            urlutils.invalid_url_error(self._win_id, url, "start download")
            return
        req = QNetworkRequest(url)
        reply = page.networkAccessManager().get(req)
        self.fetch(reply)

    def prompt_save(self, win_id, url):
        """Prompt for a new quickmark name to be added and add it.

        Args:
            win_id: The current window ID.
            url: The quickmark url as a QUrl.
        """
        if not url.isValid():
            urlutils.invalid_url_error(win_id, url, "save quickmark")
            return
        urlstr = url.toString(QUrl.RemovePassword | QUrl.FullyEncoded)
        message.ask_async(
            win_id, "Add quickmark:", usertypes.PromptMode.text,
            functools.partial(self.quickmark_add, win_id, urlstr))

    def prompt_save(self, url):
        """Prompt for a new quickmark name to be added and add it.

        Args:
            url: The quickmark url as a QUrl.
        """
        if not url.isValid():
            urlutils.invalid_url_error(url, "save quickmark")
            return
        urlstr = url.toString(QUrl.RemovePassword | QUrl.FullyEncoded)
        message.ask_async(
            "Add quickmark:", usertypes.PromptMode.text,
            functools.partial(self.quickmark_add, urlstr),
            text="Please enter a quickmark name for<br/><b>{}</b>".format(
                html.escape(url.toDisplayString())), url=urlstr)

    def get(self, url, **kwargs):
        """Start a download with a link URL.

        Args:
            url: The URL to get, as QUrl
            **kwargs: passed to get_request().

        Return:
            The created DownloadItem.
        """
        if not url.isValid():
            urlutils.invalid_url_error(self._win_id, url, "start download")
            return
        req = QNetworkRequest(url)
        return self.get_request(req, **kwargs)

    def get(self, url, **kwargs):
        """Start a download with a link URL.

        Args:
            url: The URL to get, as QUrl
            **kwargs: passed to get_request().

        Return:
            If the download could start immediately, (fileobj/filename given),
            the created DownloadItem.

            If not, None.
        """
        if not url.isValid():
            urlutils.invalid_url_error(self._win_id, url, "start download")
            return
        req = QNetworkRequest(url)
        return self.get_request(req, **kwargs)

    def get(self, url, *, user_agent=None, **kwargs):
        """Start a download with a link URL.

        Args:
            url: The URL to get, as QUrl
            user_agent: The UA to set for the request, or None.
            **kwargs: passed to get_request().

        Return:
            The created DownloadItem.
        """
        if not url.isValid():
            urlutils.invalid_url_error(url, "start download")
            return None
        req = QNetworkRequest(url)
        if user_agent is not None:
            req.setHeader(QNetworkRequest.UserAgentHeader, user_agent)
        return self.get_request(req, **kwargs)