Add distinct option to show full (assertion) diffs always

[blueyed]

Currently you have to use -vv to show the whole diff for dicts, and not to truncate in general.

Code:

• pytest/src/_pytest/assertion/util.py

  Lines 295 to 296 in c00d934

  	if same and verbose < 2:
  	explanation += [u("Omitting %s identical items, use -vv to show") % len(same)]

• pytest/src/_pytest/assertion/truncate.py

  Lines 27 to 32 in c00d934

  	def _should_truncate_item(item):
  	"""
  	Whether or not this test item is eligible for truncation.
  	"""
  	verbose = item.config.option.verbose
  	return verbose < 2 and not _running_on_ci()

1. there should be a distinct option additionally, because I usually have to re-run the test with -vv then, but would rather have it by default - without using very verbose mode by default

2. pytest.assertion.truncate checks if it is running on CI and enables this then always. This should also be done for comparing dicts anyway. Should I file a separate issue / create a PR for this already?

I would like to add this to the config file for projects where it makes sense, e.g. https://github.com/Vimjas/covimerage, where most of the tests are comparing program output (by lines), which usually gets truncated.
-vv would still have the same effect of course.

[cheezman34]

A potential workaround that might work for some:

Add to your conftest.py

from _pytest.assertion.util import assertrepr_compare
def pytest_assertrepr_compare(config, op, left, right):
    # hack the verbosity so we always show full diffs on assertion failures,
    # even if we're otherwise not fully verbose
    config.option.verbose = 2
    return assertrepr_compare(config, op, left, right)

[blueyed]

The hack does not for truncation via saferepr unfortunately (for a overlong assertion message itself).

See also #2382 and #3693.

This is really frustrating, but at least --assert=plain can be used to get the full assertion message.

[blueyed]

@pytest-dev/contributors
Any input on this (given that there are already some WIP PRs to fix issues in this regard), please?

[blueyed]

btw/JFI: for skipping truncation (just one part of it), you can use CI=true as a workaround:

pytest/src/_pytest/assertion/truncate.py

Lines 23 to 34 in cbe3e3e

	def _should_truncate_item(item):
	"""
	Whether or not this test item is eligible for truncation.
	"""
	verbose = item.config.option.verbose
	return verbose < 2 and not _running_on_ci()
	def _running_on_ci():
	"""Check if we're currently running on a CI system."""
	env_vars = ["CI", "BUILD_NUMBER"]
	return any(var in os.environ for var in env_vars)