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final fullstop. If long, they may contain newlines to break the text.
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Do not use the Python ``assert`` statement, either in tests or elsewhere.
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A source test checks that it is not used. It is ok to explicitly raise
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* It makes the behaviour vary depending on whether bzr is run with -O
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or not, therefore giving a chance for bugs that occur in one case or
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the other, several of which have already occurred: assertions with
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side effects, code which can't continue unless the assertion passes,
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cases where we should give the user a proper message rather than an
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* It's not that much shorter than an explicit if/raise.
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* It tends to lead to fuzzy thinking about whether the check is
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actually needed or not, and whether it's an internal error or not
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* It tends to cause look-before-you-leap patterns.
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* It's unsafe if the check is needed to protect the integrity of the
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* It tends to give poor messages since the developer can get by with
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no explanatory text at all.
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* We can't rely on people always running with -O in normal use, so we
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can't use it for tests that are actually expensive.
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* Expensive checks that help developers are better turned on from the
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test suite or a -D flag.
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* If used instead of ``self.assert*()`` in tests it makes them falsely pass with -O.
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Documenting Changes
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564
===================
added
removed
doc/developers/HACKING.txt
