test(radio-tile): add unit tests

tests/RadioTile/RadioTile.group.test.svelte

@@ -0,0 +1,25 @@
+<script lang="ts">
+  import { TileGroup, RadioTile, Button } from "carbon-components-svelte";
+
+  const values = ["Lite plan", "Standard plan", "Plus plan"];
+
+  let selected = values[1];
+</script>
+
+<TileGroup legend="Service pricing tiers" name="plan" bind:selected>
+  {#each values as value}
+    <RadioTile {value}>{value}</RadioTile>
+  {/each}
+</TileGroup>
+
+<div>
+  Selected: {selected}
+</div>
+
+<Button
+  size="small"
+  disabled={selected === values[1]}
+  on:click={() => (selected = values[1])}
+>
+  Set to "{values[1]}"
+</Button>