Initial code commit

.gitignore

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+node_modules
+dist

index.js

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+import execa from 'execa'
+
+export default function execaHelper (cli, throwOnStdErr = true) {
+  return async function withCli (t, run) {
+    await run(t, async (...params) => {
+      const result = await execa(cli, params)
+
+      // Throw an error if stderr has content so that the test fails.
+      if (throwOnStdErr && result.stderr) {
+        throw new Error(result.stderr)
+      }
+
+      return result
+    })
+  }
+}

package.json

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+{
+  "name": "@ianwalter/execa-helper",
+  "description": "An AVA helper that makes it easier to test CLIs using Execa",
+  "module": "dist/execa-helper.m.js",
+  "main": "dist/execa-helper.js",
+  "scripts": {
+    "lint": "eslint index.js test.js",
+    "pretest": "dist",
+    "test": "ava"
+  },
+  "dependencies": {
+    "execa": "^1.0.0"
+  },
+  "devDependencies": {
+    "@ianwalter/dist": "^1.4.0",
+    "ava": "^1.1.0",
+    "eslint": "^5.12.0",
+    "eslint-config-standard": "^12.0.0",
+    "eslint-plugin-html": "^5.0.0",
+    "eslint-plugin-import": "^2.14.0",
+    "eslint-plugin-node": "^8.0.1",
+    "eslint-plugin-promise": "^4.0.1",
+    "eslint-plugin-standard": "^4.0.0",
+    "meow": "^5.0.0",
+    "np": "^4.0.2"
+  },
+  "eslintConfig": {
+    "root": true,
+    "extends": [
+      "eslint:recommended",
+      "standard"
+    ]
+  }
+}

test/cli

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+#!/usr/bin/env node
+
+const meow = require('meow')
+
+const cli = meow(
+  `
+    Usage
+      $ cli <options>
+
+    Options
+      --from, -f      Author of the greeting
+      --greeting, -g  Output a greeting
+
+    Examples
+      $ cli --from Ian --greeting Hello World!
+      [Ian]: Hello World!
+  `,
+  {
+    flags: {
+      from: { type: 'string', alias: 'f' },
+      greeting: { type: 'string', alias: 'g' }
+    }
+  }
+)
+
+if (!cli.flags.from) {
+  console.error('No author specified!')
+}
+
+console.log(`[${cli.flags.from}]: ${cli.flags.greeting}`)

test/snapshots/test.js.md

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+# Snapshot report for `test/test.js`
+
+The actual snapshot is saved in `test.js.snap`.
+
+Generated by [AVA](https://ava.li).
+
+## doesn't throw error when configured
+
+> Snapshot 1
+
+    '[undefined]: Hello World!'
+
+> Snapshot 2
+
+    'No author specified!'
+
+## returns stdout when stderr has no content
+
+> Snapshot 1
+
+    '[Ian]: Hello World!'

test/test.js

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+import test from 'ava'
+import execaHelper from '..'
+
+const withCli = execaHelper('./test/cli')
+const withNoThrowCli = execaHelper('./test/cli', false)
+
+test('throws error when stderr has content', withCli, async (t, cli) => {
+  await t.throwsAsync(async () => cli('--greeting', 'Hello World!'))
+})
+
+test('returns stdout when stderr has no content', withCli, async (t, cli) => {
+  const { stdout } = await cli('--from', 'Ian', '--greeting', 'Hello World!')
+  t.snapshot(stdout)
+})
+
+test(`doesn't throw error when configured`, withNoThrowCli, async (t, cli) => {
+  const { stdout, stderr } = await cli('--greeting', 'Hello World!')
+  t.snapshot(stdout)
+  t.snapshot(stderr)
+})