1 files changed, 91 insertions, 0 deletions
diff --git a/packages/backend/test/unit/misc/diff-arrays.ts b/packages/backend/test/unit/misc/diff-arrays.ts
new file mode 100644
index 0000000000..b6db5e2eca
--- /dev/null
+++ b/packages/backend/test/unit/misc/diff-arrays.ts
@@ -0,0 +1,91 @@
+/*
+ * SPDX-FileCopyrightText: hazelnoot and other Sharkey contributors
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { diffArrays, diffArraysSimple } from '@/misc/diff-arrays.js';
+
+describe(diffArrays, () => {
+	it('should return empty result when both inputs are null', () => {
+		const result = diffArrays(null, null);
+		expect(result.added).toHaveLength(0);
+		expect(result.removed).toHaveLength(0);
+	});
+
+	it('should return empty result when both inputs are empty', () => {
+		const result = diffArrays([], []);
+		expect(result.added).toHaveLength(0);
+		expect(result.removed).toHaveLength(0);
+	});
+
+	it('should remove before when after is empty', () => {
+		const result = diffArrays([1, 2, 3], []);
+		expect(result.added).toHaveLength(0);
+		expect(result.removed).toEqual([1, 2, 3]);
+	});
+
+	it('should deduplicate before when after is empty', () => {
+		const result = diffArrays([1, 1, 2, 2, 3], []);
+		expect(result.added).toHaveLength(0);
+		expect(result.removed).toEqual([1, 2, 3]);
+	});
+
+	it('should add after when before is empty', () => {
+		const result = diffArrays([], [1, 2, 3]);
+		expect(result.added).toEqual([1, 2, 3]);
+		expect(result.removed).toHaveLength(0);
+	});
+
+	it('should deduplicate after when before is empty', () => {
+		const result = diffArrays([], [1, 1, 2, 2, 3]);
+		expect(result.added).toEqual([1, 2, 3]);
+		expect(result.removed).toHaveLength(0);
+	});
+
+	it('should return diff when both have values', () => {
+		const result = diffArrays(
+			['a', 'b', 'c', 'd'],
+			['a', 'c', 'e', 'f'],
+		);
+		expect(result.added).toEqual(['e', 'f']);
+		expect(result.removed).toEqual(['b', 'd']);
+	});
+});
+
+describe(diffArraysSimple, () => {
+	it('should return false when both inputs are null', () => {
+		const result = diffArraysSimple(null, null);
+		expect(result).toBe(false);
+	});
+
+	it('should return false when both inputs are empty', () => {
+		const result = diffArraysSimple([], []);
+		expect(result).toBe(false);
+	});
+
+	it('should return true when before is populated and after is empty', () => {
+		const result = diffArraysSimple([1, 2, 3], []);
+		expect(result).toBe(true);
+	});
+
+	it('should return true when before is empty and after is populated', () => {
+		const result = diffArraysSimple([], [1, 2, 3]);
+		expect(result).toBe(true);
+	});
+
+	it('should return true when values have changed', () => {
+		const result = diffArraysSimple(
+			['a', 'a', 'b', 'c'],
+			['a', 'b', 'c', 'd'],
+		);
+		expect(result).toBe(true);
+	});
+
+	it('should return false when values have not changed', () => {
+		const result = diffArraysSimple(
+			['a', 'a', 'b', 'c'],
+			['a', 'b', 'c', 'c'],
+		);
+		expect(result).toBe(false);
+	});
+});