'Handle singular matrices.
GH-2228'

def test_singular_matrices(self):

    table = Table(Domain([ContinuousVariable('a'), ContinuousVariable('b')], class_vars=DiscreteVariable('c', values=['0', '1'])), list(zip([1, 1, 1], [0, 1, 2], [0, 1, 1])))
    self.send_signal(self.widget.Inputs.data, table)
    self.widget.manifold_methods_combo.activated.emit(0)
    self.widget.tsne_editor.metric_combo.activated.emit(4)
    self.assertFalse(self.widget.Error.manifold_error.is_shown())
    self.widget.apply_button.button.click()
    self.assertTrue(self.widget.Error.manifold_error.is_shown())
