unify usage of sleepAsync and add tests

The tests mock JS setTimeout API. However promise.resolve() is not working without flushing the promise queue (which could be done just by awaiting Promise.resolve()), similar issue has been discussed in facebook/jest#2157.

tests/unit/infrastructure/Threading/AsyncLazy.spec.ts

@@ -0,0 +1,53 @@
+import 'mocha';
+import { expect } from 'chai';
+import { AsyncLazy } from '@/infrastructure/Threading/AsyncLazy';
+import { sleepAsync } from '@/infrastructure/Threading/AsyncSleep';
+
+describe('AsyncLazy', () => {
+    it('returns value from lambda', async () => {
+        // arrange
+        const expected = 'test';
+        const lambda = () => Promise.resolve(expected);
+        const sut = new AsyncLazy(lambda);
+        // act
+        const actual = await sut.getValueAsync();
+        // assert
+        expect(actual).to.equal(expected);
+    });
+    describe('when running multiple times', () => {
+        // arrange
+        let totalExecuted: number = 0;
+        beforeEach(() => totalExecuted = 0);
+        it('when running sync', async () => {
+            // act
+            const sut = new AsyncLazy(() => {
+                totalExecuted++;
+                return Promise.resolve(totalExecuted);
+            });
+            const results = new Array<number>();
+            for (let i = 0; i < 5; i++) {
+                results.push(await sut.getValueAsync());
+            }
+            // assert
+            expect(totalExecuted).to.equal(1);
+            expect(results).to.deep.equal([1, 1, 1, 1, 1]);
+        });
+        it('when running long-running task in parallel', async () => {
+            // act
+            const sut = new AsyncLazy(async () => {
+                await sleepAsync(100);
+                totalExecuted++;
+                return Promise.resolve(totalExecuted);
+            });
+            const results = await Promise.all([
+                sut.getValueAsync(),
+                sut.getValueAsync(),
+                sut.getValueAsync(),
+                sut.getValueAsync(),
+                sut.getValueAsync()]);
+            // assert
+            expect(totalExecuted).to.equal(1);
+            expect(results).to.deep.equal([1, 1, 1, 1, 1]);
+        });
+    });
+});