test(expandable-tile): add unit tests

tests/ExpandableTile/ExpandableTileCustom.test.svelte

@@ -0,0 +1,31 @@
+<script lang="ts">
+  import { ExpandableTile, Button } from "carbon-components-svelte";
+
+  export let buttonClicked = false;
+  export let linkClicked = false;
+</script>
+
+<ExpandableTile tileExpandedLabel="View less" tileCollapsedLabel="View more">
+  <div slot="above">
+    <a
+      href="/"
+      data-testid="test-link"
+      on:click|preventDefault|stopPropagation={() => {
+        linkClicked = true;
+      }}
+    >
+      Test link
+    </a>
+    <br /><br />
+    <Button
+      data-testid="test-button"
+      on:click={(e) => {
+        e.stopPropagation();
+        buttonClicked = true;
+      }}
+    >
+      Test button
+    </Button>
+  </div>
+  <div slot="below">Below the fold content here</div>
+</ExpandableTile>