Proposal: Should we include a matcher?

[orta]

I had a fail based on two long strings which I fixed this way:

After putting a console.log in the dangerfile. This ain't good.

---

Code looked like this:

import dtsGenerator from "./scripts/danger-dts"
const currentDTS = dtsGenerator()
const savedDTS = fs.readFileSync("source/danger.d.ts").toString()
if (currentDTS !== savedDTS) {
  const message = "There are changes to the Danger DSL which are not reflected in the current danger.d.ts."
  const idea = "Please run <code>yarn declarations</code> and update this PR."
  fail(`${message}<br/><i>${idea}</i>`)
}

We already have jest-diff inside the app, due to jest-config, so what about instead we provide something like:

import dtsGenerator from "./scripts/danger-dts"
const currentDTS = dtsGenerator()
const savedDTS = fs.readFileSync("source/danger.d.ts").toString()

const message = "There are changes to the Danger DSL which are not reflected in the current danger.d.ts."
const idea = "Please run <code>yarn declarations</code> and update this PR."
const failureMessage =`${message}<br/><i>${idea}</i>`

danger.utils.checkEqual(fail, failureMessage, currentDTS, savedDTS)

Where we can present jest-matcher like messages inline. For example:

or

[orta]

Messages could look like:

	Warnings
⚠️	There are changes to the Danger DSL which are not reflected in the current danger.d.ts. Please run yarn declarations and update this PR.

Expected:
+  "<a href=\"https://github.com/artsy/emission/blob/new/a/b/c\">a/b/c</a> and <a href=\"https://github.com/orta/emission/blob/new/d/e/f\">d/e/f</a>"
Received:
-  "<a href=\"https://github.com/orta/emission/blob/new/a/b/c\">a/b/c</a> and <a href=\"https://github.com/orta/emission/blob/new/d/e/f\">d/e/f</a>"

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