diff --git a/tests/dedupeBadges.test.ts b/tests/dedupeBadges.test.ts
new file mode 100644
index 0000000..103db9d
--- /dev/null
+++ b/tests/dedupeBadges.test.ts
@@ -0,0 +1,39 @@
+import { describe, expect, it } from 'vitest';
+import { dedupeBadges } from '../src/api/avatar/dedupeBadges';
+
+describe('dedupeBadges', () =>
+{
+    it('returns an empty array for an empty input', () =>
+    {
+        expect(dedupeBadges([])).toEqual([]);
+    });
+
+    it('preserves unique badges in slot order', () =>
+    {
+        expect(dedupeBadges([ 'a', 'b', 'c' ])).toEqual([ 'a', 'b', 'c' ]);
+    });
+
+    it('replaces duplicate slots with empty strings to preserve slot indices', () =>
+    {
+        expect(dedupeBadges([ 'a', 'b', 'a', 'c' ])).toEqual([ 'a', 'b', '', 'c' ]);
+    });
+
+    it('normalizes falsy entries (null, undefined, "") to empty string', () =>
+    {
+        // server sometimes returns null/undefined for unused slots
+        const input = [ 'a', null as unknown as string, '', undefined as unknown as string, 'b' ];
+
+        expect(dedupeBadges(input)).toEqual([ 'a', '', '', '', 'b' ]);
+    });
+
+    it('only keeps the FIRST occurrence of each unique code', () =>
+    {
+        expect(dedupeBadges([ 'a', 'a', 'a' ])).toEqual([ 'a', '', '' ]);
+    });
+
+    it('is order-sensitive: identical multisets but different orderings yield different outputs', () =>
+    {
+        expect(dedupeBadges([ 'a', 'b', 'a' ])).toEqual([ 'a', 'b', '' ]);
+        expect(dedupeBadges([ 'b', 'a', 'a' ])).toEqual([ 'b', 'a', '' ]);
+    });
+});