LFUCache/LRUCache : convert live code example to Jest test.

Cache/test/LFUCache.test.js

@@ -0,0 +1,54 @@
+import { LFUCache } from '../LFUCache'
+
+describe('LFUCache', () => {
+  it('Example 1 (Small Cache, size=2)', () => {
+    const cache = new LFUCache(2)
+    cache.set(1, 1)
+    cache.set(2, 2)
+
+    expect(cache.get(1)).toBe(1)
+    expect(cache.get(2)).toBe(2)
+
+    // Additional entries triggers cache rotate
+    cache.set(3, 3)
+
+    // Then we should have a cache miss for the first entry added
+    expect(cache.get(1)).toBe(null)
+    expect(cache.get(2)).toBe(2)
+    expect(cache.get(3)).toBe(3)
+
+    cache.set(4, 4)
+    expect(cache.get(1)).toBe(null) // cache miss
+    expect(cache.get(2)).toBe(null) // cache miss
+    expect(cache.get(3)).toBe(3)
+    expect(cache.get(4)).toBe(4)
+
+    expect(cache.cacheInfo()).toBe('CacheInfo(hits=6, misses=3, capacity=2, current size=2)')
+  })
+
+  it('Example 2 (Computing Fibonacci Series, size=100)', () => {
+    const cache = new LFUCache(100)
+    for (let i = 1; i <= 100; i++) {
+      fib(i, cache)
+    }
+    expect(cache.cacheInfo()).toBe('CacheInfo(hits=193, misses=103, capacity=100, current size=98)')
+  })
+})
+
+// Helper for building and caching Fibonacci series
+function fib (num, cache = null) {
+  if (cache) {
+    const value = cache.get(num)
+    if (value) {
+      return value
+    }
+  }
+  if (num === 1 || num === 2) {
+    return 1
+  }
+  const result = fib(num - 1, cache) + fib(num - 2, cache)
+  if (cache) {
+    cache.set(num, result)
+  }
+  return result
+}