test(combo-box): add unit tests

tests/ComboBox/ComboBoxCustom.test.svelte

@@ -0,0 +1,36 @@
+<script lang="ts">
+  import { ComboBox } from "carbon-components-svelte";
+  import type { ComboBoxItem } from "carbon-components-svelte/ComboBox/ComboBox.svelte";
+
+  let comboBoxRef: ComboBox;
+
+  export let items: ComboBoxItem[] = [
+    { id: "0", text: "Slack" },
+    { id: "1", text: "Email" },
+    { id: "2", text: "Fax", disabled: true },
+  ];
+  export let selectedId: string | undefined = undefined;
+  export let direction: "top" | "bottom" = "bottom";
+  export let shouldFilterItem = (item: ComboBoxItem, value: string) =>
+    item.text.toLowerCase().includes(value.toLowerCase());
+  export let itemToString = (item: ComboBoxItem) => item.text;
+</script>
+
+<ComboBox
+  bind:this={comboBoxRef}
+  {items}
+  {selectedId}
+  {direction}
+  {shouldFilterItem}
+  {itemToString}
+  titleText="Contact with icons"
+  placeholder="Select contact method"
+  on:select={(e) => {
+    console.log("select", e.detail);
+  }}
+  let:item
+>
+  <span>Item {item.text}</span>
+</ComboBox>
+
+<button type="button" on:click={() => comboBoxRef.clear()}>Clear</button>