feat(sandbox): expose interface to create async flush scheduler

Author: kwonoj

src/RxAsyncSandboxInstance.ts

@@ -0,0 +1,3 @@
+interface RxAsyncSandboxInstance {}
+
+export { RxAsyncSandboxInstance };

src/RxSandbox.ts

@@ -1,7 +1,8 @@
 import { SubscriptionLog } from 'rxjs/dist/types/internal/testing/SubscriptionLog';
 import { TestMessage } from './message/TestMessage';
+import { RxAsyncSandboxInstance } from './RxAsyncSandboxInstance';
 import { RxSandboxInstance } from './RxSandboxInstance';
-import { SandboxOption } from './SandboxOption';
+import { AsyncFlushSandboxOption, SandboxOption } from './SandboxOption';
 
 export interface RxSandbox {
   /**
@@ -11,6 +12,7 @@ export interface RxSandbox {
    * @return {RxSandboxInstance} instance of test scheduler interfaces.
    */
   create(autoFlush?: boolean, frameTimeFactor?: number, maxFrameValue?: number): RxSandboxInstance;
+  create(options: AsyncFlushSandboxOption): RxAsyncSandboxInstance;
   create(options?: Partial<SandboxOption>): RxSandboxInstance;
   /**
    * Utility assertion method to assert marble based observable test messages.

src/RxSandboxInstance.ts

@@ -14,7 +14,7 @@ type expectedObservable = <T = string>(
 ) => Readonly<Array<TestMessage<T | Array<TestMessage<T>>>>>;
 type expectedSubscription = (marble: string) => SubscriptionLog;
 
-type RxSandboxInstance = {
+interface RxSandboxInstance {
   /**
    * Test scheduler created for sandbox instance
    */
@@ -49,7 +49,7 @@ type RxSandboxInstance = {
    * Utility function to generate `expected` subscriptions via marble diagram.
    */
   s: expectedSubscription;
-};
+}
 
 export {
   hotObservable,

src/SandboxOption.ts

@@ -18,4 +18,14 @@ interface SandboxOption {
   maxFrameValue: number;
 }
 
-export { SandboxOption };
+interface AsyncFlushSandboxOption extends Partial<SandboxOption> {
+  /**
+   * Scheduling each actions into next available tick when flush
+   * along with native promises chained in inner observables.
+   *
+   * Scheduler's flush will no longer resolve synchronously.
+   */
+  flushWithAsyncTick: true;
+}
+
+export { SandboxOption, AsyncFlushSandboxOption };