Track / monitor test failures and core dump in FileWidget

[ntoll]

This issue has been created to track random crashes in the test suite when exercising event_filter method of FileWidget. The original comment left in the code on that method is:

        # HERE BE DRAGONS.
        # The checks for "not self.downloading" in the following lines of code
        # probably look strange. The obvious thing to do is to wrap such a
        # check as a conditional. However, for reasons that are not entirely
        # clear, this regularly caused random crashes when running the test
        # suite (on Ubuntu 18.04, Python3.7). The following code expresses the
        # same logic but without causing the random the crash of the test
        # suite.
        if t == QEvent.HoverEnter and not self.downloading:
            self.download_button.setIcon(load_icon('download_file_hover.svg'))
        elif t == QEvent.HoverLeave and not self.downloading:
            self.download_button.setIcon(load_icon('download_file.svg'))
        return QObject.event(obj, event)

[ntoll]

Ref #792 for context.

[gonzalo-bulnes]

Taking a mental note of this because I noticed that the FileWidget's test suite may be destroying QThread instances without stopping the thread first. That typically results in a Python core dump.

I don't know if the crashes you observed @ntoll are related to that, but I'm planning on addressing the thread management issue. (See #1510)