raise UsageError on magic not found

avoids reporting failed execution as success

and test that errors in magics report as execution failures

IPython/core/interactiveshell.py

@@ -2076,7 +2076,7 b' class InteractiveShell(SingletonConfigurable):'
             etpl = "Line magic function `%%%s` not found%s."
             extra = '' if cm is None else (' (But cell magic `%%%%%s` exists, '
                                     'did you mean that instead?)' % magic_name )
-            error(etpl % (magic_name, extra))
+            raise UsageError(etpl % (magic_name, extra))
         else:
             # Note: this is the distance in the stack to the user's frame.
             # This will need to be updated if the internal calling logic gets
@@ -2115,7 +2115,7 b' class InteractiveShell(SingletonConfigurable):'
             etpl = "Cell magic `%%{0}` not found{1}."
             extra = '' if lm is None else (' (But line magic `%{0}` exists, '
                             'did you mean that instead?)'.format(magic_name))
-            error(etpl.format(magic_name, extra))
+            raise UsageError(etpl.format(magic_name, extra))
         elif cell == '':
             message = '%%{0} is a cell magic, but the cell body is empty.'.format(magic_name)
             if self.find_line_magic(magic_name) is not None:

IPython/core/tests/test_magic.py

@@ -74,6 +74,35 b' def test_extract_symbols_raises_exception_with_non_python_code():'
     with nt.assert_raises(SyntaxError):
         code.extract_symbols(source, "hello")
 
+
+def test_magic_not_found():
+    # magic not found raises UsageError
+    with nt.assert_raises(UsageError):
+        _ip.magic('doesntexist')
+
+    # ensure result isn't success when a magic isn't found
+    result = _ip.run_cell('%doesntexist')
+    assert isinstance(result.error_in_exec, UsageError)
+
+
+def test_cell_magic_not_found():
+    # magic not found raises UsageError
+    with nt.assert_raises(UsageError):
+        _ip.run_cell_magic('doesntexist', 'line', 'cell')
+
+    # ensure result isn't success when a magic isn't found
+    result = _ip.run_cell('%%doesntexist')
+    assert isinstance(result.error_in_exec, UsageError)
+
+
+def test_magic_error_status():
+    def fail(shell):
+        1/0
+    _ip.register_magic_function(fail)
+    result = _ip.run_cell('%fail')
+    assert isinstance(result.error_in_exec, ZeroDivisionError)
+
+
 def test_config():
     """ test that config magic does not raise
     can happen if Configurable init is moved too early into