Add AVA testing infra (GoogleChrome#110)

* wip

* Get ava linting working.

* Add tests for links.js

Author: robdodson

.eslintrc.js

@@ -0,0 +1,28 @@
+module.exports = {
+  extends: ['./node_modules/gts', 'plugin:ava/recommended'],
+  parserOptions: {
+    sourceType: 'module',
+  },
+  rules: {
+    // By default AVA will ignore folders or files with underscores in
+    // their name. Since we have test paths like /site/_data/… we need to
+    // disable this linter rule and enable these paths in our ava.config.js.
+    'ava/no-ignored-test-files': 0,
+
+    // This rule checks to if your package requires devDependencies.
+    // This rule is useful if you're publishing a package to npm but we're not,
+    // we're building an application and we require devDependencies in a lot of
+    // places. For our use case it makes sense to disable this rule.
+    // Read more: https://github.com/mysticatea/eslint-plugin-node/issues/47
+    'node/no-unpublished-require': 0,
+
+    // This rule looks at the node version in your package.json's engines field
+    // to determine which ES features are allowed. Our engine field says we
+    // support Node v12 which does not yet have support for modules. But we use
+    // rollup to bundle our client-side JS and our config.js files for other
+    // tools like ava and rollup support ESM.
+    'node/no-unsupported-features/es-syntax': ['error', {
+      'ignores': ['modules'],
+    }]
+  }
+};

.eslintrc.json

@@ -9,6 +9,10 @@ Thumbs.db
 .env
 .cache
 
+# Code coverage generated files
+.nyc_output
+coverage
+
 # Node modules and output
 node_modules
 dist

.gitignore

@@ -0,0 +1,7 @@
+export default {
+  files: ['tests/**/*'],
+  // This needs to be turned on to let AVA use power-assert for enhanced
+  // assertion messages.
+  // Read more: https://github.com/avajs/ava/blob/master/docs/03-assertions.md#enhanced-assertion-messages
+  babel: true,
+};