Avoid truncation when it makes the output longer #6267
Description
Pytest version 3.10.1, also seen on Ubuntu 19.04:
With -v, when the output of a failure is close to the truncation limit, verbosity is increased, and the extra words are not useful. In short, this:
$ py.test-3 -v | wc
60 269 3287
$ py.test-3 -vv | wc
59 272 3292
In addition the truncation message is misleading in the number of truncated lines. With -v:
E assert b'<!DOCTYPE H...cation.</p>\n' == b'{}'
E At index 0 diff: 60 != 123
E Left contains more items, first extra item: 68
E Full diff:
E + b'{}'
E - (b'<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">\n<title>500 Inter'
E - b'nal Server Error</title>\n<h1>Internal Server Error</h1>\n<p>The server en'
E - b'countered an internal error and was unable to complete your request. Either'...
E
E ...Full output truncated (2 lines hidden), use '-vv' to show
With -vv:
E assert b'<!DOCTYPE H...cation.</p>\n' == b'{}'
E At index 0 diff: 60 != 123
E Left contains more items, first extra item: 68
E Full diff:
E + b'{}'
E - (b'<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">\n<title>500 Inter'
E - b'nal Server Error</title>\n<h1>Internal Server Error</h1>\n<p>The server en'
E - b'countered an internal error and was unable to complete your request. Either'
E - b' the server is overloaded or there is an error in the application.</p>\n')
That looks one extra line to me, not two. Possibly lines are counted by splitting on \n, and the message has a terminating \n, technically leaving an empty line at the end -- but this empty line is not shown in the -vv output.
it would be better for pytest to print the one line of error, rather than the two lines making an inaccurate claim about the truncation.