It would be easy to add unit test command

[orklann]

Thank you for the great extension, is it possible to make a quick fix to add unit test command, I think adding a test() function after this line:

https://github.com/sterin/vscode-xcodebuild-tools/blob/master/py/xcodebuild_tools.py#L112

    def test(self):
        self.xcodebuild('test')

would make it work, except that I don't know how to call this function in the UI.