code: def test_raises(self):
      with self.test_session():
          X1 = tf.constant([[0.0]])
          X2 = tf.constant([[0.0]])
          lengthscale = tf.constant(-5.0)
          variance = tf.constant(-1.0)
          with self.assertRaisesOpError("Condition"):
              rbf(X1, X2, variance=variance).eval()
              rbf(X1, X2, lengthscale).eval()
              rbf(X1, X2, lengthscale, variance).eval()
  
file_path: edward/tests/util/rbf_test.py
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import numpy
  import tensorflow
  from edward.util import rbf
label_desc: Use image node_id 6 for calling the test_rbf_class obj's underlying member method code with example usage: obj.test_raises() without return types