Add circular effect scheduler regression test

Author: joshhanley

tests/cypress/integration/directives/x-effect.spec.js

@@ -0,0 +1,19 @@
+import { html, test } from '../../utils'
+
+test('effects that trigger each other do not requeue endlessly in the same flush',
+    [html`
+        <div x-data="{ a: 0, b: 0 }">
+            <button @click="window.__allowCircularEffects = true; a++">start</button>
+
+            <span x-effect="a; if (window.__allowCircularEffects) { if (++window.__circularEffectRuns > 4) throw new Error('Circular effects requeued endlessly'); b++ }"></span>
+            <span x-effect="b; if (window.__allowCircularEffects) { if (++window.__circularEffectRuns > 4) throw new Error('Circular effects requeued endlessly'); a++ }"></span>
+        </div>
+    `,
+    `
+        window.__allowCircularEffects = false
+        window.__circularEffectRuns = 0
+    `],
+    ({ get }) => {
+        get('button').click()
+    }
+)