Use assert statements in tests

Make assert statements print pretty output, including source.

This makes assert x == y more usable, as an alternative to self.assertEqual(x, y)

This plugin implements outcomeDetail() and checks for event.exc_info If it finds that an AssertionError happened, it will inspect the traceback and add additional detail to the error report.

Configuration [pretty-assert]

always-on

Default: False
Type: boolean

Sample configuration

The default configuration is equivalent to including the following in a unittest.cfg file.

[pretty-assert]
always-on = False

Command-line options

--pretty-assert DEFAULT: Add pretty output for “assert” statements

Plugin class reference: PrettyAssert

class nose2.plugins.prettyassert.PrettyAssert(*args, **kwargs)[source]

Add pretty output for “assert” statements

static addAssertDetail(extraDetail, exc, trace)[source]

Add details to output regarding AssertionError and its context

extraDetail: a list of lines which will be joined with newlines and added to the output for this test failure – defined as part of the event format

exc: the AssertionError exception which was thrown

trace: a traceback object for the exception

assert statement inspection

The prettyassert plugin works by inspecting the stack frame which raised an AssertionError. Unlike pytest’s assertion rewriting code, it does not modify the built-in AssertionError.

As a result, it is somewhat limited in its capabilities – it can only report the bound values from that stack frame. That means that this type of statement works well:

x = f()
y = g()
assert x == y

but this type of statement does not:

assert f() == g()

It will still run, but the prettyassert will tell you that f and g are functions, not what they evaluated to. This is probably not what you want.

attribute resolution

The assertion inspection will resolve attributes, so that expressions like this will work as well:

assert x.foo == 1

But note that the attribute x.foo will be resolved twice in this case, if the assertion fails. Once when the assertion is evaluated, and again when it is inspected.

As a result, properties with dynamic values may not behave as expected under prettyassert inspection.