Performance runner

[ngryman]

0.3.0 will offer a way to integrate SR in a classic development workflow. The aim of this version is to provide an easy way to track any performance regression.

Snapshots

A new command will be introduced: test. It will act like the run command but for a different purpose: see if all races are as fast or faster than before.

In order to achieve this, we'll introduce the concept of snapshots for SR. Like test runners offering a snapshot feature, SR will create and save a report snapshot for each race on the first run. Subsequent runs will compare new reports with their snapshot and display appropriate results.

If the new report is as fast or faster, the test is considered as passed. If not, a diff will be displayed and the test command will return a non-zero error code.

Visual diff

The visual diff should be clear enough to highlight the parts where the run has been slower. Because reports are a DSL, we'll use an in-house diffing/display mechanism instead of a general purpose one (i.e. jest-snapshot).