From 24ca2f6c416e5c3f55ea7d646be6661eddf12851 Mon Sep 17 00:00:00 2001
From: Ilia Mashkov <hikkikomori7@gmail.com>
Date: Wed, 18 Feb 2026 20:17:33 +0300
Subject: [PATCH] test(throttle): add unit tests for throttle util

---
 .../lib/utils/throttle/throttle.test.ts       | 319 ++++++++++++++++++
 1 file changed, 319 insertions(+)
 create mode 100644 src/shared/lib/utils/throttle/throttle.test.ts

diff --git a/src/shared/lib/utils/throttle/throttle.test.ts b/src/shared/lib/utils/throttle/throttle.test.ts
new file mode 100644
index 0000000..b22d5ac
--- /dev/null
+++ b/src/shared/lib/utils/throttle/throttle.test.ts
@@ -0,0 +1,319 @@
+import {
+    afterEach,
+    beforeEach,
+    describe,
+    expect,
+    it,
+    vi,
+} from 'vitest';
+import { throttle } from './throttle';
+
+describe('throttle', () => {
+    beforeEach(() => {
+        vi.useFakeTimers();
+    });
+
+    afterEach(() => {
+        vi.restoreAllMocks();
+        vi.useRealTimers();
+    });
+
+    describe('Basic Functionality', () => {
+        it('should execute function immediately on first call', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 300);
+
+            throttled('arg1', 'arg2');
+
+            expect(mockFn).toHaveBeenCalledTimes(1);
+            expect(mockFn).toHaveBeenCalledWith('arg1', 'arg2');
+        });
+
+        it('should throttle subsequent calls within wait period', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 300);
+
+            throttled('first');
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            // Call again within wait period - should not execute
+            throttled('second');
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            // Advance time past wait period
+            vi.advanceTimersByTime(300);
+
+            // Now trailing call executes
+            expect(mockFn).toHaveBeenCalledTimes(2);
+            expect(mockFn).toHaveBeenLastCalledWith('second');
+        });
+
+        it('should allow execution after wait period expires', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            throttled('first');
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            vi.advanceTimersByTime(100);
+            throttled('second');
+
+            expect(mockFn).toHaveBeenCalledTimes(2);
+        });
+    });
+
+    describe('Trailing Edge Execution', () => {
+        it('should execute throttled call after wait period', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 300);
+
+            throttled('first');
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            throttled('second');
+            throttled('third');
+            // Still 1 because these are throttled
+
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            vi.advanceTimersByTime(300);
+
+            // Trailing call executes
+            expect(mockFn).toHaveBeenCalledTimes(2);
+            expect(mockFn).toHaveBeenLastCalledWith('third');
+        });
+
+        it('should cancel previous trailing call on new invocation', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            throttled('first');
+            vi.advanceTimersByTime(50);
+            throttled('second');
+            vi.advanceTimersByTime(30);
+            throttled('third');
+
+            // At this point only first call executed
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            // Advance to trigger trailing call
+            vi.advanceTimersByTime(70);
+
+            // First call + trailing (third)
+            expect(mockFn).toHaveBeenCalledTimes(2);
+            expect(mockFn).toHaveBeenLastCalledWith('third');
+        });
+    });
+
+    describe('Arguments and Context', () => {
+        it('should pass the correct arguments from the last throttled call', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            throttled('arg1', 'arg2');
+            vi.advanceTimersByTime(50);
+            throttled('arg3', 'arg4');
+            vi.advanceTimersByTime(100);
+
+            expect(mockFn).toHaveBeenCalledTimes(2);
+            expect(mockFn).toHaveBeenLastCalledWith('arg3', 'arg4');
+        });
+
+        it('should handle no arguments', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            throttled();
+
+            expect(mockFn).toHaveBeenCalledTimes(1);
+        });
+
+        it('should handle single argument', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            throttled('single');
+
+            expect(mockFn).toHaveBeenCalledTimes(1);
+            expect(mockFn).toHaveBeenCalledWith('single');
+        });
+
+        it('should handle multiple arguments', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            throttled(1, 2, 3, 'four', { five: 5 });
+
+            expect(mockFn).toHaveBeenCalledTimes(1);
+            expect(mockFn).toHaveBeenCalledWith(1, 2, 3, 'four', { five: 5 });
+        });
+    });
+
+    describe('Timing', () => {
+        it('should handle very short wait times (1ms)', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 1);
+
+            throttled('first');
+            vi.advanceTimersByTime(1);
+            throttled('second');
+
+            expect(mockFn).toHaveBeenCalledTimes(2);
+        });
+
+        it('should handle longer wait times (1000ms)', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 1000);
+
+            throttled('first');
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            vi.advanceTimersByTime(500);
+            throttled('second');
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            vi.advanceTimersByTime(500);
+            expect(mockFn).toHaveBeenCalledTimes(2);
+        });
+    });
+
+    describe('Rapid Calls', () => {
+        it('should handle rapid successive calls correctly', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            throttled('call1');
+            vi.advanceTimersByTime(10);
+            throttled('call2');
+            vi.advanceTimersByTime(10);
+            throttled('call3');
+            vi.advanceTimersByTime(10);
+
+            expect(mockFn).toHaveBeenCalledTimes(1);
+            expect(mockFn).toHaveBeenCalledWith('call1');
+
+            vi.advanceTimersByTime(100);
+
+            expect(mockFn).toHaveBeenCalledTimes(2);
+            expect(mockFn).toHaveBeenLastCalledWith('call3');
+        });
+
+        it('should execute function at most once per wait period plus trailing', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            // Make many rapid calls
+            for (let i = 0; i < 10; i++) {
+                vi.advanceTimersByTime(5);
+                throttled(`call${i}`);
+            }
+
+            // Should execute immediately
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            vi.advanceTimersByTime(100);
+
+            // Plus trailing call
+            expect(mockFn).toHaveBeenCalledTimes(2);
+        });
+    });
+
+    describe('Edge Cases', () => {
+        it('should handle zero wait time', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 0);
+
+            throttled('first');
+
+            // With zero wait time, function may execute synchronously
+            // but the internal timing may still prevent immediate re-execution
+            expect(mockFn).toHaveBeenCalledTimes(1);
+        });
+
+        it('should handle being called at exactly wait boundary', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 100);
+
+            throttled('first');
+            vi.advanceTimersByTime(100);
+            throttled('second');
+
+            expect(mockFn).toHaveBeenCalledTimes(2);
+        });
+    });
+
+    describe('Return Value', () => {
+        it('should not return anything (void)', () => {
+            const mockFn = vi.fn().mockReturnValue('result');
+            const throttled = throttle(mockFn, 100);
+
+            const result = throttled('arg');
+
+            expect(result).toBeUndefined();
+        });
+    });
+
+    describe('Real-World Scenarios', () => {
+        it('should throttle scroll-like events', () => {
+            const mockFn = vi.fn();
+            const throttledScroll = throttle(mockFn, 100);
+
+            throttledScroll();
+            vi.advanceTimersByTime(10);
+            throttledScroll();
+            vi.advanceTimersByTime(10);
+            throttledScroll();
+            vi.advanceTimersByTime(10);
+
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            vi.advanceTimersByTime(100);
+            expect(mockFn).toHaveBeenCalledTimes(2);
+        });
+
+        it('should throttle resize-like events', () => {
+            const mockFn = vi.fn();
+            const throttledResize = throttle(mockFn, 200);
+
+            throttledResize();
+            for (let i = 1; i <= 10; i++) {
+                vi.advanceTimersByTime(10);
+                throttledResize();
+            }
+
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            vi.advanceTimersByTime(200);
+            expect(mockFn).toHaveBeenCalledTimes(2);
+        });
+    });
+
+    describe('Comparison Characteristics', () => {
+        it('should execute immediately on first call', () => {
+            const mockFn = vi.fn();
+            const throttled = throttle(mockFn, 300);
+
+            throttled('first');
+
+            // Throttle executes immediately (unlike debounce)
+            expect(mockFn).toHaveBeenCalledTimes(1);
+        });
+
+        it('should allow execution during continuous calls at intervals', () => {
+            const mockFn = vi.fn();
+            const waitTime = 100;
+            const throttled = throttle(mockFn, waitTime);
+
+            throttled('call1');
+            expect(mockFn).toHaveBeenCalledTimes(1);
+
+            vi.advanceTimersByTime(waitTime);
+            throttled('call2');
+            expect(mockFn).toHaveBeenCalledTimes(2);
+
+            vi.advanceTimersByTime(waitTime);
+            throttled('call3');
+            expect(mockFn).toHaveBeenCalledTimes(3);
+        });
+    });
+});