fix handling of asserts for python3

lib/spack/spack/error.py

@@ -22,10 +22,12 @@ def re_raise(e, exc_info=None):
 
     # construct arguments to re-raise error from type
     args = []
-    if hasattr(e, 'message'):
+    if hasattr(e, 'args'):
+        args.extend(e.args)
+    if hasattr(e, 'message') and e.message not in e.args:
         args.append(e.message)
     if hasattr(e, 'long_message'):
-        args.append(e.long_message)
+        args.append(str(e.long_message))
 
     if sys.version_info[0] < 3:
         # ugly hack: exec to avoid the fact this is a syntax

lib/spack/spack/test/cmd/test.py

@@ -88,6 +88,7 @@ def test_test_output_on_failure(mock_packages, mock_archive, mock_fetch,
         out = spack_test('test-fail', fail_on_error=False)
 
     assert "Expected 'not in the output' in output of `true`" in out
+    assert "AssertionError:" in out
 
 
 def test_show_log_on_error(mock_packages, mock_archive, mock_fetch,