test(button): add unit tests

tests/Button/Button.test.svelte

@@ -0,0 +1,45 @@
+<script lang="ts">
+  import { Button } from "carbon-components-svelte";
+  import Add from "carbon-icons-svelte/lib/Add.svelte";
+</script>
+
+<Button>primary</Button>
+<Button kind="secondary">secondary</Button>
+<Button kind="tertiary">tertiary</Button>
+<Button kind="ghost">ghost</Button>
+<Button kind="danger">danger</Button>
+<Button kind="danger-tertiary">danger-tertiary</Button>
+<Button kind="danger-ghost">danger-ghost</Button>
+
+<Button size="field">field size</Button>
+<Button size="small">small size</Button>
+
+<Button
+  icon={Add}
+  tooltipPosition="bottom"
+  tooltipAlignment="center"
+  iconDescription="Tooltip text"
+/>
+
+<Button href="#">Link button</Button>
+
+<Button as let:props>
+  <p {...props}>Custom element</p>
+</Button>
+
+<Button disabled>Disabled button</Button>
+
+<Button icon={Add}>With icon</Button>
+
+<Button
+  data-testid="btn"
+  on:click={() => {
+    console.log("click");
+  }}
+>
+  Test button
+</Button>
+
+<Button skeleton />
+<Button skeleton size="field" />
+<Button skeleton size="small" />