refactor: Use ES6, Test with AVA

- Use async/await instead of callbacks
- Use execa to run command line
- Use AVA for tests
- Add several assertions in the unit tests
- Add documentation (comments) in the tests
- Run tests with a real git repo instead of mocking child_process and add test helpers to create repos, commits and checkout
- Simplify test directory structure
- Simplify code readability (mostly with async/await)
- Use eslint for for linting, prettier for formatting

package.json

@@ -1,6 +1,6 @@
 {
   "name": "semantic-release",
-  "description": "automated semver compliant package publishing",
+  "description": "Automated semver compliant package publishing",
   "version": "0.0.0-placeholder",
   "author": "Stephan Bönnemann <stephan@boennemann.me> (http://boennemann.me)",
   "bin": {
@@ -20,38 +20,60 @@
     "@semantic-release/error": "^2.0.0",
     "@semantic-release/last-release-npm": "^2.0.0",
     "@semantic-release/release-notes-generator": "^4.0.0",
+    "execa": "^0.8.0",
+    "fs-extra": "^4.0.2",
     "git-head": "^1.2.1",
-    "github": "^8.0.0",
+    "github": "^11.0.0",
     "lodash": "^4.0.0",
     "nerf-dart": "^1.0.0",
     "nopt": "^4.0.0",
     "normalize-package-data": "^2.3.4",
     "npmconf": "^2.1.2",
     "npmlog": "^4.0.0",
+    "p-series": "^1.0.0",
     "parse-github-repo-url": "^1.3.0",
     "require-relative": "^0.8.7",
-    "run-auto": "^2.0.0",
-    "run-series": "^1.1.3",
-    "semver": "^5.2.0"
+    "semver": "^5.4.1"
   },
   "devDependencies": {
     "coveralls": "^3.0.0",
+    "ava": "^0.22.0",
+    "commitizen": "^2.9.6",
     "cz-conventional-changelog": "^2.0.0",
-    "mkdirp": "^0.5.1",
-    "mock-spawn": "^0.2.6",
-    "nixt": "^0.5.0",
+    "eslint": "^4.7.0",
+    "eslint-config-prettier": "^2.5.0",
+    "eslint-config-standard": "^10.2.1",
+    "eslint-plugin-import": "^2.7.0",
+    "eslint-plugin-node": "^5.2.0",
+    "eslint-plugin-prettier": "^2.3.0",
+    "eslint-plugin-promise": "^3.5.0",
+    "eslint-plugin-standard": "^3.0.1",
     "nock": "^9.0.2",
     "npm-registry-couchapp": "^2.6.12",
-    "nyc": "^10.0.0",
+    "nyc": "^11.2.1",
+    "p-map-series": "^1.0.0",
+    "prettier": "^1.7.0",
     "proxyquire": "^1.7.3",
     "rimraf": "^2.5.0",
-    "standard": "^9.0.0",
-    "tap": "^10.0.1"
+    "sinon": "^4.0.0",
+    "tempy": "^0.2.1"
   },
   "engines": {
     "node": ">=4",
     "npm": ">=2"
   },
+  "eslintConfig": {
+    "extends": [
+      "standard",
+      "prettier"
+    ],
+    "plugins": [
+      "prettier"
+    ],
+    "rules": {
+      "prettier/prettier": 2
+    }
+  },
   "files": [
     "bin",
     "src"
@@ -70,6 +92,23 @@
   ],
   "license": "MIT",
   "main": "bin/semantic-release.js",
+  "nyc": {
+    "include": [
+      "src/**/*.js"
+    ],
+    "reporter": [
+      "json",
+      "text",
+      "html"
+    ],
+    "all": true
+  },
+  "prettier": {
+    "printWidth": 120,
+    "singleQuote": true,
+    "bracketSpacing": false,
+    "trailingComma": "es5"
+  },
   "publishConfig": {
     "tag": "next"
   },
@@ -83,10 +122,11 @@
   "scripts": {
     "coverage": "nyc report",
     "coverage:upload": "npm run coverage -s -- --reporter=text-lcov | coveralls",
-    "pretest": "standard",
+    "clean": "rimraf coverage && rimraf .nyc_output",
+    "cm": "git-cz",
+    "lint": "eslint .",
+    "pretest": "npm run clean && npm run lint",
     "semantic-release": "./bin/semantic-release.js pre && npm publish && ./bin/semantic-release.js post",
-    "test": "npm run test:unit && npm run test:integration",
-    "test:integration": "tap --no-cov test/scenarios/*.js",
-    "test:unit": "nyc tap --no-cov test/specs/*.js"
+    "test": "nyc ava -v"
   }
 }