Fix unit test (aws#32)

Author: ChoiByungWook

tests/unit/test_tuner.py

@@ -140,7 +140,7 @@ def test_stop_tuning_job(sagemaker_session, tuner):
 def test_stop_tuning_job_no_tuning_job(tuner):
     with pytest.raises(ValueError) as e:
             tuner.stop_tuning_job()
-    assert 'No HPO job available' in str(e)
+    assert 'No tuning job available' in str(e)
 
 
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