Add custom config tests

babel.config.js

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+/**
+ * This file is only needed for test.js where we import JSX (with .js extension).
+ * Consumers of the shared ESLint config do not need to install and configure Babel
+ * to use the config.
+ */
+
+export default {
+  presets: [
+    [
+      '@babel/preset-react',
+      {
+        runtime: 'automatic',
+      },
+    ],
+  ],
+};

examples/fail/no-unsed-vars.js

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+const foo = 'bar';
+
+export default [/'foo' is assigned a value but never used/];

examples/fail/use-effect-event.js

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+import React, {useEffectEvent} from 'react';
+
+export function BadComponent() {
+  return <button onClick={useEffectEvent(() => false)}>click me</button>;
+}
+
+export default [
+  /React Hook "useEffectEvent" can only be called at the top level of your component/,
+];