feature/cache: Add basic lru-cache tests

Author: Intellicode

src/__snapshots__/lru-cache.spec.js.snap

@@ -0,0 +1,21 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`Lru .constructor() constructs the cache properly 1`] = `
+LRU {
+  "cache": LRUCache {
+    Symbol(max): 10,
+    Symbol(lengthCalculator): [Function],
+    Symbol(allowStale): false,
+    Symbol(maxAge): 0,
+    Symbol(dispose): undefined,
+    Symbol(noDisposeOnSet): false,
+    Symbol(cache): Map {},
+    Symbol(lruList): Yallist {
+      "head": null,
+      "length": 0,
+      "tail": null,
+    },
+    Symbol(length): 0,
+  },
+}
+`;

src/lru-cache.spec.js

@@ -0,0 +1,99 @@
+const Lru = require('./lru-cache');
+
+describe('Lru', () => {
+  describe('.constructor()', () => {
+    it('constructs the cache properly', () => {
+      const actual = new Lru({ maxItems: 10 });
+      expect(actual).toMatchSnapshot();
+    });
+  });
+
+  describe('.get(key)', () => {
+    let instance;
+    const maxItems = 10;
+
+    beforeEach(() => {
+      instance = new Lru({ maxItems });
+    });
+
+    it('returns a promise', () => {
+      const actual = instance.get('key');
+      expect(actual).toBeInstanceOf(Promise);
+    });
+
+    it('returns undefined when the key is not set', () => {
+      expect.assertions(1);
+      return instance.get('key').then(actual => expect(actual).toBeUndefined());
+    });
+
+    it('returns the correct item when the key is set', () => {
+      const expected = 'hello world';
+      expect.assertions(1);
+      return instance
+        .set('key', expected)
+        .then(() => instance.get('key'))
+        .then(actual => expect(actual).toEqual(expected));
+    });
+
+    it('returns undefined when the key is ejected', () => {
+      const expected = 'hello world';
+      const range = Array.from(new Array(maxItems), (x, i) => i);
+
+      expect.assertions(1);
+
+      return instance
+        .set('key', expected)
+        .then(() =>
+          Promise.all(range.map(i => instance.set(`key${i}`, 'hello universe')))
+        )
+        .then(() => instance.get('key'))
+        .then(actual => expect(actual).toEqual(undefined));
+    });
+  });
+
+  describe('.set(key, value, options)', () => {
+    let instance;
+    const maxItems = 10;
+
+    beforeEach(() => {
+      instance = new Lru({ maxItems });
+    });
+
+    it('increments the item count', () => {
+      expect.assertions(1);
+      return instance
+        .set('key', 'value')
+        .then(() => expect(instance.length()).toEqual(1));
+    });
+
+    it('adheres to maxItems when more items are inserted', () => {
+      const range = Array.from(new Array(maxItems + 1), (x, i) => i);
+
+      expect.assertions(1);
+
+      return Promise.all(
+        range.map(i => instance.set(`key${i}`, 'hello universe'))
+      ).then(() => expect(instance.length()).toEqual(maxItems));
+    });
+
+    it('only stores the last items in order of last insertion', () => {
+      const range = Array.from(new Array(maxItems), (x, i) => i);
+
+      expect.assertions(1);
+
+      return instance
+        .set('key', 'value')
+        .then(() =>
+          Promise.all(
+            range.map(i => instance.set(`key${i}`, `hello universe ${i}`))
+          )
+        )
+        .then(() => instance.values())
+        .then(values =>
+          expect(values).toEqual(
+            range.map(i => `hello universe ${i}`).reverse()
+          )
+        );
+    });
+  });
+});