add Completion class

test/console/completion.test.js

@@ -0,0 +1,48 @@
+import { expect } from "chai";
+import Completion from '../../src/console/completion';
+
+describe('Completion class', () => {
+  describe('#constructor', () => {
+    it('creates new object by iterable items', () => {
+      new Completion([1,2,3,4,5]);
+      new Completion([]);
+      new Completion('hello');
+      new Completion('');
+    });
+
+    it('creates new object by iterable items', () => {
+      expect(() => new Completion({ key: 'value' })).to.throw(TypeError);
+      expect(() => new Completion(12345)).to.throw(TypeError);
+    });
+  });
+
+  describe('#next', () => {
+    it('complete next items', () => {
+      let completion = new Completion([3, 4, 5]);
+      expect(completion.next()).to.equal(3);
+      expect(completion.next()).to.equal(4);
+      expect(completion.next()).to.equal(5);
+      expect(completion.next()).to.equal(3);
+    });
+
+    it('returns null when empty completions', () => {
+      let completion = new Completion([]);
+      expect(completion.next()).to.be.null;
+    });
+  });
+
+  describe('#prev', () => {
+    it('complete prev items', () => {
+      let completion = new Completion([3, 4, 5]);
+      expect(completion.prev()).to.equal(5);
+      expect(completion.prev()).to.equal(4);
+      expect(completion.prev()).to.equal(3);
+      expect(completion.prev()).to.equal(5);
+    });
+
+    it('returns null when empty completions', () => {
+      let completion = new Completion([]);
+      expect(completion.prev()).to.be.null;
+    });
+  });
+});