Updatable tests (thanks @DylanVann)

test/test.ts

@@ -1,24 +1,42 @@
 import test from 'ava'
 import { sync } from 'glob'
-import { readFile } from 'mz/fs'
+import { readFile, writeFile } from 'mz/fs'
 import { basename, resolve } from 'path'
 import { compile } from '../src'
 
 let paths = ['e2e', 'rules', 'unit']
 
+// Kind of hacky thing to figure out if -u or --update-snapshots was passed to AVA.
+// We manually write expected output in this test.
+// It's more clear, and allows us to have input and output files for each test.
+const argvString = process.env.npm_config_argv as string
+const argv = JSON.parse(argvString || '')
+const argvOriginal = argv.original || []
+const update =
+  argvOriginal.includes('-u') || argvOriginal.includes('--update-snapshots')
+
 paths.forEach(path => {
   // TODO: Why does glob catch tslint.json even with the trailing slash?
-  let folders = sync(resolve(__dirname, `../../test/${path}/*/`))
+  const folders = sync(resolve(__dirname, `../../test/${path}/*/`))
     .filter(_ => !_.endsWith('.json'))
     .filter(_ => !basename(_).startsWith('_'))
 
-  folders.forEach(folder =>
-    test(basename(folder), async t => {
+  const tests = folders.map(folder => ({ folder, name: basename(folder) }))
+
+  tests.forEach(({ name, folder }) =>
+    test(name, async t => {
       try {
-        let filein = resolve(folder, 'input.txt')
-        let input = await readFile(filein, 'utf-8')
-        let output = await readFile(resolve(folder, 'output.txt'), 'utf-8')
-        t.is(await compile(input, filein), output)
+        const inputPath = resolve(folder, 'input.txt')
+        const outputPath = resolve(folder, 'output.txt')
+        const input = await readFile(inputPath, 'utf-8')
+        const output = await compile(input, inputPath)
+        if (update) {
+          await writeFile(outputPath, output)
+          t.pass()
+        } else {
+          const expectedOutput = await readFile(outputPath, 'utf-8')
+          t.is(output, expectedOutput)
+        }
       } catch (e) {
         console.log('error', e)
       }