Possible performance improvement: Generate messages only if assertions fail

[dhardtke]

Since serializing large objects can sometimes take some time it would be neat if Earl would generate messages lazily, i.e., only if an assertion fails.

For example, instead of:

https://github.com/l2beat/earl/blob/ea923158550558c46336f0a1038ad522ec62cc43/packages/earl/src/validators/basic/toBeTruthy.ts#L38C1-L45C2

let's do something like this:

export function toBeTruthy(control: Control) {
  control.assert({
    success: truthy()(control.actual),
    reason: () => `The value ${formatCompact(control.actual)} is not truthy, but it was expected to be truthy.`,
    negatedReason: () => `The value ${formatCompact(control.actual)} is truthy, but it was expected not to be truthy.`,
  })
}

I do not have benchmarks to back this claim up but I don't see why it wouldn't lead to a substantial performance gain.

[canab]

I have tested earl on some large project. It results in 15...20% slower run (comparing with should.js)

Quick testing the @dhardtke idea shows at least 50% better execution time on expect(object).toEqual(...)

CPU snapshot shows that most time is consumed by formatCompact and preapreStackTrace. As I understand, the execution of those functions is only required if test fails. Avoiding them should result in significant performance boost.

[canab]

I've created a pull request https://github.com/l2beat/earl/pull/296 Only toEqual function has been modified and synthetic test run time is reduced from 800ms to 15ms