tests: improve for GeneratePermutations (TheAlgorithms#1263)

Author: kho-kho-kho

Backtracking/tests/GeneratePermutations.test.js

@@ -1,14 +1,33 @@
+import { factorial } from '../../Recursive/Factorial'
 import { permutations } from '../GeneratePermutations'
 
 describe('Permutations', () => {
+  it('Permutations of [a]', () => {
+    const perms = permutations(['a'])
+    expect(perms).toHaveLength(factorial(1))
+    expect(perms).toContainEqual(['a'])
+  })
+
+  it('Permutations of [true, false]', () => {
+    const perms = permutations([true, false])
+    expect(perms).toHaveLength(factorial(2))
+    expect(perms).toContainEqual([true, false])
+    expect(perms).toContainEqual([false, true])
+  })
+
   it('Permutations of [1, 2, 3]', () => {
-    expect(permutations([1, 2, 3])).toEqual([
-      [1, 2, 3],
-      [1, 3, 2],
-      [2, 1, 3],
-      [2, 3, 1],
-      [3, 1, 2],
-      [3, 2, 1]
-    ])
+    const perms = permutations([1, 2, 3])
+    expect(perms).toHaveLength(factorial(3))
+    expect(perms).toContainEqual([1, 2, 3])
+    expect(perms).toContainEqual([1, 3, 2])
+    expect(perms).toContainEqual([2, 1, 3])
+    expect(perms).toContainEqual([2, 3, 1])
+    expect(perms).toContainEqual([3, 1, 2])
+    expect(perms).toContainEqual([3, 2, 1])
+  })
+
+  it('Permutation counts across larger input arrays', () => {
+    expect(permutations([1, 2, 3, 4, 5, 6, 7, 8])).toHaveLength(factorial(8))
+    expect(permutations([1, 2, 3, 4, 5, 6, 7, 8, 9])).toHaveLength(factorial(9))
   })
 })