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Avoid truncation when truncating means longer output (#10446) 

Fixes #6267
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Pierre Sassoulas 2022-12-17 14:24:46 +01:00 committed by GitHub
parent f6adebb990
commit b31db4809b
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4 changed files with 86 additions and 37 deletions
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1
AUTHORS
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@ -280,6 +280,7 @@ Paweł Adamczak
Pedro Algarvio
Petter Strandmark
Philipp Loose
Pierre Sassoulas
Pieter Mulder
Piotr Banaszkiewicz
Piotr Helm

2
changelog/6267.improvement.rst Normal file
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@ -0,0 +1,2 @@
The full output of a test is no longer truncated if the truncation message would be longer than
the hidden text. The line number shown has also been fixed.

71
src/_pytest/assertion/truncate.py
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@ -38,9 +38,9 @@ def _truncate_explanation(
"""Truncate given list of strings that makes up the assertion explanation.
Truncates to either 8 lines, or 640 characters - whichever the input reaches
first. The remaining lines will be replaced by a usage message.
first, taking the truncation explanation into account. The remaining lines
will be replaced by a usage message.
"""
if max_lines is None:
max_lines = DEFAULT_MAX_LINES
if max_chars is None:
@ -48,35 +48,56 @@ def _truncate_explanation(
# Check if truncation required
input_char_count = len("".join(input_lines))
if len(input_lines) <= max_lines and input_char_count <= max_chars:
# The length of the truncation explanation depends on the number of lines
# removed but is at least 68 characters:
# The real value is
# 64 (for the base message:
# '...\n...Full output truncated (1 line hidden), use '-vv' to show")'
# )
# + 1 (for plural)
# + int(math.log10(len(input_lines) - max_lines)) (number of hidden line, at least 1)
# + 3 for the '...' added to the truncated line
# But if there's more than 100 lines it's very likely that we're going to
# truncate, so we don't need the exact value using log10.
tolerable_max_chars = (
max_chars + 70 # 64 + 1 (for plural) + 2 (for '99') + 3 for '...'
)
# The truncation explanation add two lines to the output
tolerable_max_lines = max_lines + 2
if (
len(input_lines) <= tolerable_max_lines
and input_char_count <= tolerable_max_chars
):
return input_lines
# Truncate first to max_lines, and then truncate to max_chars if max_chars
# is exceeded.
# Truncate first to max_lines, and then truncate to max_chars if necessary
truncated_explanation = input_lines[:max_lines]
truncated_explanation = _truncate_by_char_count(truncated_explanation, max_chars)
# Add ellipsis to final line
truncated_explanation[-1] = truncated_explanation[-1] + "..."
# Append useful message to explanation
truncated_line_count = len(input_lines) - len(truncated_explanation)
truncated_line_count += 1 # Account for the part-truncated final line
msg = "...Full output truncated"
if truncated_line_count == 1:
msg += f" ({truncated_line_count} line hidden)"
truncated_char = True
# We reevaluate the need to truncate chars following removal of some lines
if len("".join(truncated_explanation)) > tolerable_max_chars:
truncated_explanation = _truncate_by_char_count(
truncated_explanation, max_chars
)
else:
msg += f" ({truncated_line_count} lines hidden)"
msg += f", {USAGE_MSG}"
truncated_explanation.extend(["", str(msg)])
return truncated_explanation
truncated_char = False
truncated_line_count = len(input_lines) - len(truncated_explanation)
if truncated_explanation[-1]:
# Add ellipsis and take into account part-truncated final line
truncated_explanation[-1] = truncated_explanation[-1] + "..."
if truncated_char:
# It's possible that we did not remove any char from this line
truncated_line_count += 1
else:
# Add proper ellipsis when we were able to fit a full line exactly
truncated_explanation[-1] = "..."
return truncated_explanation + [
"",
f"...Full output truncated ({truncated_line_count} line"
f"{'' if truncated_line_count == 1 else 's'} hidden), {USAGE_MSG}",
]
def _truncate_by_char_count(input_lines: List[str], max_chars: int) -> List[str]:
# Check if truncation required
if len("".join(input_lines)) <= max_chars:
return input_lines
# Find point at which input length exceeds total allowed length
iterated_char_count = 0
for iterated_index, input_line in enumerate(input_lines):

49
testing/test_assertion.py
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@ -807,9 +807,9 @@ class TestAssert_reprcompare_dataclass:
"E ['field_b']",
"E ",
"E Drill down into differing attribute field_b:",
"E field_b: 'b' != 'c'...",
"E ",
"E ...Full output truncated (3 lines hidden), use '-vv' to show",
"E field_b: 'b' != 'c'",
"E - c",
"E + b",
],
consecutive=True,
)
@ -827,7 +827,7 @@ class TestAssert_reprcompare_dataclass:
"E Drill down into differing attribute g:",
"E g: S(a=10, b='ten') != S(a=20, b='xxx')...",
"E ",
"E ...Full output truncated (52 lines hidden), use '-vv' to show",
"E ...Full output truncated (51 lines hidden), use '-vv' to show",
],
consecutive=True,
)
@ -1188,30 +1188,55 @@ class TestTruncateExplanation:
def test_truncates_at_8_lines_when_given_list_of_empty_strings(self) -> None:
expl = ["" for x in range(50)]
result = truncate._truncate_explanation(expl, max_lines=8, max_chars=100)
assert len(result) != len(expl)
assert result != expl
assert len(result) == 8 + self.LINES_IN_TRUNCATION_MSG
assert "Full output truncated" in result[-1]
assert "43 lines hidden" in result[-1]
assert "42 lines hidden" in result[-1]
last_line_before_trunc_msg = result[-self.LINES_IN_TRUNCATION_MSG - 1]
assert last_line_before_trunc_msg.endswith("...")
def test_truncates_at_8_lines_when_first_8_lines_are_LT_max_chars(self) -> None:
expl = ["a" for x in range(100)]
total_lines = 100
expl = ["a" for x in range(total_lines)]
result = truncate._truncate_explanation(expl, max_lines=8, max_chars=8 * 80)
assert result != expl
assert len(result) == 8 + self.LINES_IN_TRUNCATION_MSG
assert "Full output truncated" in result[-1]
assert "93 lines hidden" in result[-1]
assert f"{total_lines - 8} lines hidden" in result[-1]
last_line_before_trunc_msg = result[-self.LINES_IN_TRUNCATION_MSG - 1]
assert last_line_before_trunc_msg.endswith("...")
def test_truncates_at_8_lines_when_there_is_one_line_to_remove(self) -> None:
"""The number of line in the result is 9, the same number as if we truncated."""
expl = ["a" for x in range(9)]
result = truncate._truncate_explanation(expl, max_lines=8, max_chars=8 * 80)
assert result == expl
assert "truncated" not in result[-1]
def test_truncates_edgecase_when_truncation_message_makes_the_result_longer_for_chars(
self,
) -> None:
line = "a" * 10
expl = [line, line]
result = truncate._truncate_explanation(expl, max_lines=10, max_chars=10)
assert result == [line, line]
def test_truncates_edgecase_when_truncation_message_makes_the_result_longer_for_lines(
self,
) -> None:
line = "a" * 10
expl = [line, line]
result = truncate._truncate_explanation(expl, max_lines=1, max_chars=100)
assert result == [line, line]
def test_truncates_at_8_lines_when_first_8_lines_are_EQ_max_chars(self) -> None:
expl = ["a" * 80 for x in range(16)]
expl = [chr(97 + x) * 80 for x in range(16)]
result = truncate._truncate_explanation(expl, max_lines=8, max_chars=8 * 80)
assert result != expl
assert len(result) == 8 + self.LINES_IN_TRUNCATION_MSG
assert len(result) == 16 - 8 + self.LINES_IN_TRUNCATION_MSG
assert "Full output truncated" in result[-1]
assert "9 lines hidden" in result[-1]
assert "8 lines hidden" in result[-1]
last_line_before_trunc_msg = result[-self.LINES_IN_TRUNCATION_MSG - 1]
assert last_line_before_trunc_msg.endswith("...")
@ -1240,7 +1265,7 @@ class TestTruncateExplanation:
line_count = 7
line_len = 100
expected_truncated_lines = 2
expected_truncated_lines = 1
pytester.makepyfile(
r"""
def test_many_lines():
@ -1261,7 +1286,7 @@ class TestTruncateExplanation:
"*+ 1*",
"*+ 3*",
"*+ 5*",
"*truncated (%d lines hidden)*use*-vv*" % expected_truncated_lines,
"*truncated (%d line hidden)*use*-vv*" % expected_truncated_lines,
]
)