test: add function test cases (#10)

* test: add function test cases

* chore(function.spec.ts): upd the import path of `function.spec.ts`

tests/function.spec.ts

@@ -0,0 +1,70 @@
+import { describe, it, expect, vi } from 'vitest'
+import { debounce, throttle, call } from '../src'
+
+describe('Utility Functions', () => {
+  describe('debounce', () => {
+    it('should call the function after the specified delay', async () => {
+      const fn = vi.fn()
+      const debouncedFn = debounce(fn, 100)
+
+      debouncedFn()
+      debouncedFn()
+      debouncedFn()
+
+      await new Promise((resolve) => setTimeout(resolve, 150))
+
+      expect(fn).toHaveBeenCalledTimes(1)
+    })
+
+    it('should not call the function if called again before the delay', async () => {
+      const fn = vi.fn()
+      const debouncedFn = debounce(fn, 100)
+
+      debouncedFn()
+      debouncedFn()
+
+      await new Promise((resolve) => setTimeout(resolve, 150))
+
+      expect(fn).toHaveBeenCalledTimes(1)
+    })
+  })
+
+  describe('throttle', () => {
+    it('should call the function immediately and then at specified intervals', async () => {
+      const fn = vi.fn()
+      const throttledFn = throttle(fn, 100)
+
+      throttledFn()
+      throttledFn()
+      await new Promise((resolve) => setTimeout(resolve, 50))
+      throttledFn()
+      await new Promise((resolve) => setTimeout(resolve, 100))
+      throttledFn()
+
+      expect(fn).toHaveBeenCalledTimes(2)
+    })
+  })
+
+  describe('call', () => {
+    it('should call a single function with provided arguments', () => {
+      const fn = vi.fn((a: number, b: number) => a + b)
+      const result = call(fn, 1, 2)
+      expect(result).toBe(3)
+      expect(fn).toHaveBeenCalledWith(1, 2)
+    })
+
+    it('should call multiple functions and return their results', () => {
+      const fn1 = vi.fn((a: number) => a + 1)
+      const fn2 = vi.fn((a: number) => a * 2)
+      const result = call([fn1, fn2], 2)
+      expect(result).toEqual([3, 4])
+      expect(fn1).toHaveBeenCalledWith(2)
+      expect(fn2).toHaveBeenCalledWith(2)
+    })
+
+    it('should return undefined if no function is provided', () => {
+      const result = call(null, 1, 2)
+      expect(result).toBeUndefined()
+    })
+  })
+})