stretchr/testify

Diff is empty when lines are too long

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#746 opened on Mar 27, 2019

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help wanted

Description

On assert.Equal failures, if the diff has long lines (due to complicated structs), instead of showing something like

require.go:157:
                	Error Trace:	common_test.go:72
                	            				transactions_test.go:844
                	Error:      	Not equal:
					expected: ...
					actual: ...

					Diff:
					--- Expected
					+++ Actual
					<super long line...>
                	Test:       	TestTransactionsQueryFingerprint
                	Messages:   	Response does not match expected return

Currently the diff is completely cut off

require.go:157:
                	Error Trace:	common_test.go:72
                	            				transactions_test.go:844
                	Error:      	Not equal:
                	Test:       	TestTransactionsQueryFingerprint
                	Messages:   	Response does not match expected return

This makes testing hard to check which lines differed.

Upon inspecting, indentation formatting of diff lines is using bufio.Scanner which has a default MaxScanTokenSize (64K) and would not parse long lines: https://github.com/stretchr/testify/blob/master/assert/assertions.go#L201

Can be fixed by either changing from bufio.Scanner to bufio.Reader or truncating long lines up to the max token size (or even provide a config to change max). Thoughts?

Contributor guide

Tech stack
go
Domain
testing
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Go basicsBufio.Scanner knowledge
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70
Research direction
Investigate the diff formatting in assert/assertions.go line 201 where bufio.Scanner is used. Consider switching to bufio.Reader or truncating lines to avoid the MaxScanTokenSize limit. Review the function that generates the diff output and test with long lines to verify the fix.