test(splitArray): add unit tests for splitArray util

src/shared/lib/utils/splitArray/splitArray.test.ts

@@ -0,0 +1,405 @@
+import {
+    describe,
+    expect,
+    it,
+} from 'vitest';
+import { splitArray } from './splitArray';
+
+describe('splitArray', () => {
+    describe('Basic Functionality', () => {
+        it('should split an array into two arrays based on callback', () => {
+            const input = [1, 2, 3, 4, 5];
+            const [pass, fail] = splitArray(input, n => n > 2);
+
+            expect(pass).toEqual([3, 4, 5]);
+            expect(fail).toEqual([1, 2]);
+        });
+
+        it('should return two arrays', () => {
+            const result = splitArray([1, 2, 3], () => true);
+
+            expect(Array.isArray(result)).toBe(true);
+            expect(result).toHaveLength(2);
+            expect(Array.isArray(result[0])).toBe(true);
+            expect(Array.isArray(result[1])).toBe(true);
+        });
+
+        it('should preserve original array', () => {
+            const input = [1, 2, 3, 4, 5];
+            const original = [...input];
+
+            splitArray(input, n => n % 2 === 0);
+
+            expect(input).toEqual(original);
+        });
+    });
+
+    describe('Empty Array', () => {
+        it('should return two empty arrays for empty input', () => {
+            const [pass, fail] = splitArray([], () => true);
+
+            expect(pass).toEqual([]);
+            expect(fail).toEqual([]);
+        });
+
+        it('should handle empty array with falsy callback', () => {
+            const [pass, fail] = splitArray([], () => false);
+
+            expect(pass).toEqual([]);
+            expect(fail).toEqual([]);
+        });
+    });
+
+    describe('All Pass', () => {
+        it('should put all elements in pass array when callback returns true for all', () => {
+            const input = [1, 2, 3, 4, 5];
+            const [pass, fail] = splitArray(input, () => true);
+
+            expect(pass).toEqual([1, 2, 3, 4, 5]);
+            expect(fail).toEqual([]);
+        });
+
+        it('should put all elements in pass array using always-true condition', () => {
+            const input = ['a', 'b', 'c'];
+            const [pass, fail] = splitArray(input, s => s.length > 0);
+
+            expect(pass).toEqual(['a', 'b', 'c']);
+            expect(fail).toEqual([]);
+        });
+    });
+
+    describe('All Fail', () => {
+        it('should put all elements in fail array when callback returns false for all', () => {
+            const input = [1, 2, 3, 4, 5];
+            const [pass, fail] = splitArray(input, () => false);
+
+            expect(pass).toEqual([]);
+            expect(fail).toEqual([1, 2, 3, 4, 5]);
+        });
+
+        it('should put all elements in fail array using always-false condition', () => {
+            const input = ['a', 'b', 'c'];
+            const [pass, fail] = splitArray(input, s => s.length > 10);
+
+            expect(pass).toEqual([]);
+            expect(fail).toEqual(['a', 'b', 'c']);
+        });
+    });
+
+    describe('Mixed Results', () => {
+        it('should split even and odd numbers', () => {
+            const input = [1, 2, 3, 4, 5, 6];
+            const [even, odd] = splitArray(input, n => n % 2 === 0);
+
+            expect(even).toEqual([2, 4, 6]);
+            expect(odd).toEqual([1, 3, 5]);
+        });
+
+        it('should split positive and negative numbers', () => {
+            const input = [-3, -2, -1, 0, 1, 2, 3];
+            const [positive, negative] = splitArray(input, n => n >= 0);
+
+            expect(positive).toEqual([0, 1, 2, 3]);
+            expect(negative).toEqual([-3, -2, -1]);
+        });
+
+        it('should split strings by length', () => {
+            const input = ['a', 'ab', 'abc', 'abcd'];
+            const [long, short] = splitArray(input, s => s.length >= 3);
+
+            expect(long).toEqual(['abc', 'abcd']);
+            expect(short).toEqual(['a', 'ab']);
+        });
+
+        it('should split objects by property', () => {
+            interface Item {
+                id: number;
+                active: boolean;
+            }
+            const input: Item[] = [
+                { id: 1, active: true },
+                { id: 2, active: false },
+                { id: 3, active: true },
+                { id: 4, active: false },
+            ];
+            const [active, inactive] = splitArray(input, item => item.active);
+
+            expect(active).toEqual([
+                { id: 1, active: true },
+                { id: 3, active: true },
+            ]);
+            expect(inactive).toEqual([
+                { id: 2, active: false },
+                { id: 4, active: false },
+            ]);
+        });
+    });
+
+    describe('Type Safety', () => {
+        it('should work with number arrays', () => {
+            const [pass, fail] = splitArray([1, 2, 3], n => n > 1);
+
+            expect(pass).toEqual([2, 3]);
+            expect(fail).toEqual([1]);
+
+            // Type check - should be numbers
+            const sum = pass[0] + pass[1];
+            expect(sum).toBe(5);
+        });
+
+        it('should work with string arrays', () => {
+            const [pass, fail] = splitArray(['a', 'bb', 'ccc'], s => s.length > 1);
+
+            expect(pass).toEqual(['bb', 'ccc']);
+            expect(fail).toEqual(['a']);
+
+            // Type check - should be strings
+            const concatenated = pass.join('');
+            expect(concatenated).toBe('bbccc');
+        });
+
+        it('should work with boolean arrays', () => {
+            const [pass, fail] = splitArray([true, false, true], b => b);
+
+            expect(pass).toEqual([true, true]);
+            expect(fail).toEqual([false]);
+        });
+
+        it('should work with generic objects', () => {
+            interface Person {
+                name: string;
+                age: number;
+            }
+            const people: Person[] = [
+                { name: 'Alice', age: 25 },
+                { name: 'Bob', age: 30 },
+                { name: 'Charlie', age: 20 },
+            ];
+            const [adults, minors] = splitArray(people, p => p.age >= 21);
+
+            expect(adults).toEqual([
+                { name: 'Alice', age: 25 },
+                { name: 'Bob', age: 30 },
+            ]);
+            expect(minors).toEqual([{ name: 'Charlie', age: 20 }]);
+        });
+
+        it('should work with null and undefined', () => {
+            const input = [null, undefined, 1, 0, ''];
+            const [truthy, falsy] = splitArray(input, item => !!item);
+
+            expect(truthy).toEqual([1]);
+            expect(falsy).toEqual([null, undefined, 0, '']);
+        });
+    });
+
+    describe('Callback Functions', () => {
+        it('should support arrow function syntax', () => {
+            const [pass, fail] = splitArray([1, 2, 3, 4], x => x % 2 === 0);
+
+            expect(pass).toEqual([2, 4]);
+            expect(fail).toEqual([1, 3]);
+        });
+
+        it('should support regular function syntax', () => {
+            const [pass, fail] = splitArray([1, 2, 3, 4], function(x) {
+                return x % 2 === 0;
+            });
+
+            expect(pass).toEqual([2, 4]);
+            expect(fail).toEqual([1, 3]);
+        });
+
+        it('should support inline conditions', () => {
+            const input = [1, 2, 3, 4, 5];
+            const [greaterThan3, others] = splitArray(input, x => x > 3);
+
+            expect(greaterThan3).toEqual([4, 5]);
+            expect(others).toEqual([1, 2, 3]);
+        });
+    });
+
+    describe('Order Preservation', () => {
+        it('should maintain order within each resulting array', () => {
+            const input = [5, 1, 4, 2, 3];
+            const [greaterThan2, lessOrEqual] = splitArray(input, n => n > 2);
+
+            expect(greaterThan2).toEqual([5, 4, 3]);
+            expect(lessOrEqual).toEqual([1, 2]);
+        });
+
+        it('should preserve relative order for complex objects', () => {
+            interface Item {
+                id: number;
+                value: string;
+            }
+            const input: Item[] = [
+                { id: 1, value: 'a' },
+                { id: 2, value: 'b' },
+                { id: 3, value: 'c' },
+                { id: 4, value: 'd' },
+            ];
+            const [evenIds, oddIds] = splitArray(input, item => item.id % 2 === 0);
+
+            expect(evenIds).toEqual([
+                { id: 2, value: 'b' },
+                { id: 4, value: 'd' },
+            ]);
+            expect(oddIds).toEqual([
+                { id: 1, value: 'a' },
+                { id: 3, value: 'c' },
+            ]);
+        });
+    });
+
+    describe('Edge Cases', () => {
+        it('should handle single element array (truthy)', () => {
+            const [pass, fail] = splitArray([1], () => true);
+
+            expect(pass).toEqual([1]);
+            expect(fail).toEqual([]);
+        });
+
+        it('should handle single element array (falsy)', () => {
+            const [pass, fail] = splitArray([1], () => false);
+
+            expect(pass).toEqual([]);
+            expect(fail).toEqual([1]);
+        });
+
+        it('should handle two element array', () => {
+            const [pass, fail] = splitArray([1, 2], n => n === 1);
+
+            expect(pass).toEqual([1]);
+            expect(fail).toEqual([2]);
+        });
+
+        it('should handle array with duplicate values', () => {
+            const [pass, fail] = splitArray([1, 1, 2, 2, 1, 1], n => n === 1);
+
+            expect(pass).toEqual([1, 1, 1, 1]);
+            expect(fail).toEqual([2, 2]);
+        });
+
+        it('should handle zero values', () => {
+            const [truthy, falsy] = splitArray([0, 1, 0, 2], Boolean);
+
+            expect(truthy).toEqual([1, 2]);
+            expect(falsy).toEqual([0, 0]);
+        });
+
+        it('should handle NaN values', () => {
+            const input = [1, NaN, 2, NaN, 3];
+            const [numbers, nans] = splitArray(input, n => !Number.isNaN(n));
+
+            expect(numbers).toEqual([1, 2, 3]);
+            expect(nans).toEqual([NaN, NaN]);
+        });
+    });
+
+    describe('Large Arrays', () => {
+        it('should handle large arrays efficiently', () => {
+            const largeArray = Array.from({ length: 10000 }, (_, i) => i);
+            const [even, odd] = splitArray(largeArray, n => n % 2 === 0);
+
+            expect(even).toHaveLength(5000);
+            expect(odd).toHaveLength(5000);
+            expect(even[0]).toBe(0);
+            expect(even[9999]).toBeUndefined();
+            expect(even[4999]).toBe(9998);
+        });
+
+        it('should maintain correct results for all elements in large array', () => {
+            const input = Array.from({ length: 1000 }, (_, i) => i);
+            const [multiplesOf3, others] = splitArray(input, n => n % 3 === 0);
+
+            // Verify counts
+            expect(multiplesOf3).toHaveLength(334); // 0, 3, 6, ..., 999
+            expect(others).toHaveLength(666);
+
+            // Verify all multiples of 3 are in correct array
+            multiplesOf3.forEach(n => {
+                expect(n % 3).toBe(0);
+            });
+
+            // Verify no multiples of 3 are in others
+            others.forEach(n => {
+                expect(n % 3).not.toBe(0);
+            });
+        });
+    });
+
+    describe('Real-World Use Cases', () => {
+        it('should separate valid from invalid emails', () => {
+            const emails = [
+                'valid@example.com',
+                'invalid',
+                'another@test.org',
+                'not-an-email',
+                'user@domain.co.uk',
+            ];
+            const emailRegex = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
+            const [valid, invalid] = splitArray(emails, email => emailRegex.test(email));
+
+            expect(valid).toEqual([
+                'valid@example.com',
+                'another@test.org',
+                'user@domain.co.uk',
+            ]);
+            expect(invalid).toEqual(['invalid', 'not-an-email']);
+        });
+
+        it('should separate completed from pending tasks', () => {
+            interface Task {
+                id: number;
+                title: string;
+                completed: boolean;
+            }
+            const tasks: Task[] = [
+                { id: 1, title: 'Task 1', completed: true },
+                { id: 2, title: 'Task 2', completed: false },
+                { id: 3, title: 'Task 3', completed: true },
+                { id: 4, title: 'Task 4', completed: false },
+            ];
+            const [completed, pending] = splitArray(tasks, task => task.completed);
+
+            expect(completed).toHaveLength(2);
+            expect(pending).toHaveLength(2);
+            expect(completed.every(t => t.completed)).toBe(true);
+            expect(pending.every(t => !t.completed)).toBe(true);
+        });
+
+        it('should separate adults from minors by age', () => {
+            interface Person {
+                name: string;
+                age: number;
+            }
+            const people: Person[] = [
+                { name: 'Alice', age: 17 },
+                { name: 'Bob', age: 25 },
+                { name: 'Charlie', age: 16 },
+                { name: 'Diana', age: 30 },
+                { name: 'Eve', age: 18 },
+            ];
+            const [adults, minors] = splitArray(people, person => person.age >= 18);
+
+            expect(adults).toEqual([
+                { name: 'Bob', age: 25 },
+                { name: 'Diana', age: 30 },
+                { name: 'Eve', age: 18 },
+            ]);
+            expect(minors).toEqual([
+                { name: 'Alice', age: 17 },
+                { name: 'Charlie', age: 16 },
+            ]);
+        });
+
+        it('should separate truthy from falsy values', () => {
+            const mixed = [0, 1, false, true, '', 'hello', null, undefined, [], [0]];
+            const [truthy, falsy] = splitArray(mixed, Boolean);
+
+            expect(truthy).toEqual([1, true, 'hello', [], [0]]);
+            expect(falsy).toEqual([0, false, '', null, undefined]);
+        });
+    });
+});