Python unit testing: make nose show failed assertions values.

Question

Hello,

is it possible to show the assertion values that failed? It shows the traceback and what kind of exception was throw but it would more practical to know which values failed.

Example:

assert result.file == file
AssertionError

Answer 1

You can catch AssertionErrors, print some debugging info, and then reraise the error with the raise command:

try:
    assert result.file == file
except AssertionError as err:
    print('result.file: {f}'.format(f=result.file))
    print(err)
    raise

Answer 2

assert result.file == file, "%s != %s" % (result.file, file,)

That's why ugly self.assert<Foo> methods were introduced in unittest.TestCase instead of nice and short asserts: self.assert<Foo> methods know how to display failure messages.

By the way, I thought that nose do some black magic so in simple cases

assert a == b

should show meaningful error message.