Feature Request: a hook to preprocess values that crash Chai diff generation

[jedwards1211]

I've had two pain points with Chai assertions in projects that use Sequelize:

• If expect(sequelizeModelInstance)... fails, the process prints unable to find module 'pg-native' and crashes before it can format the error diff
• If expect(somethingContainingASequelizeTransaction)... fails, the process runs OOM while trying to format the error diff

Note: the default truncateThreshold isn't preventing this. I am on Chai 4, and maybe Chai 5 somehow avoids these problems, but I'm unable to try Chai 5 yet since it's pure ESM.

It would be nice to systematically solve this problem once and for all. There are several ways I could work around this:

• Turn off chai diffs globally (boo, the diffs are helpful in many cases)
• Preprocess away the problematic content of actual values I'm passing to expect with a helper function
• Create a wrapper function for expect that deeply preprocesses the actual values automatically

I don't really like any of these options; the latter two don't systematically eliminate the problem, because we would have to patch every existing test file (unless we rewire chai imports, I guess) and avoid naively using expect in new tests going forward. And also, modifying the input value could alter the assertion result -- I really just wish I could hook Chai itself to do this preprocessing between when the assertion fails and when it creates diffs.

I don't see any kind of option to do this in the docs; do you agree it would be a helpful feature?

[jedwards1211]

Oh. Looking through the code, it seems like v4 just passes a showDiff flag to AssertionError, and I guess Mocha is what does the actual diffing?

[jedwards1211]

Yep, I had to monkey-patch require('mocha/lib/utils').canonicalize.