#946 Colorize 'Expected' and 'Actual' in Assert Package + Minor Fixes: #1112, #1086 & #1231

[vaguecoder]

Summary

Colorizes error, expected, actual, test name and message of the assert failure cases for better visualization.

Changes

1. Colorizing changes in assert package as per Colorize "expected" and "actual" #946
2. Minor fix of format specifiers as per Fix interpolation using %s instead of %#v for interfaces #1112 due to conflict with colorizing changes.
3. Minor fix of format specifiers as per Use %v when formatting objects in assert.Len #1086 due to conflict with colorizing changes.
4. Minor fix of order of arguments for func InEpsilon call as per Misplaced "expected" and "actual" Arguments Inside InEpsilonSlice #1231. This was an observation and I opened this issue earlier today.

Motivation

Colorizing the output for failure cases makes it easier to visualize. This was first suggested on card #946.

Related Issues

Closes #946
Closes #1231

Additional Notes for Reviewers & Maintainers

1. Please find play link with defined failure cases for 62 functions that can be ran in local with the code associated with this PR, for review.
2. difflib is unmaintained since few years now. The required code with changes are not added in assert, in diff.go. Check if there's a better solution.

[LandonTClipp]

This has the problem of inserting color coding into the output even if stdout is not a terminal, or some kind of printer capable of understanding color sequences. Most CI/CD pipelines run outside of a terminal, so this would make the output difficult to read.

[thedaneeffect]

This has the problem of inserting color coding into the output even if stdout is not a terminal, or some kind of printer capable of understanding color sequences. Most CI/CD pipelines run outside of a terminal, so this would make the output difficult to read.

Perhaps a similar approach to log.SetFlags could be done to take this into account.

package main

import (
    "testing"
    
    "github.com/stretchr/testify/require"
)

func init() {
    require.SetFlags(require.Fcolorize)
}

func TestMyFunc(t *testing.T) {
    require.Equal(t, "Foo", "Bar")
}