docs(nx): adds docs for readAll and readFirst

packages/nx/src/nx.module.ts

@@ -2,7 +2,9 @@ import {ModuleWithProviders, NgModule} from '@angular/core';
 import {DataPersistence} from './data-persistence';
 
 /**
- * @whatItDoes Provides services simplifying enterprise Angular development.
+ * @whatItDoes Provides services for enterprise Angular applications.
+ *
+ * See {@link DataPersistence} for more information.
  */
 @NgModule({})
 export class NxModule {

packages/nx/src/testing-utils.ts

@@ -3,10 +3,34 @@ import {first} from 'rxjs/operator/first';
 import {toArray} from 'rxjs/operator/toArray';
 import {toPromise} from 'rxjs/operator/toPromise';
 
+/**
+ * @whatItDoes reads all the values from an observable and returns a promise
+ * with an array of all values. This should be used in combination with async/await.
+ *
+ * ## Example
+ *
+ * ```typescript
+ * const obs = of(1, 2, 3, 4);
+ * const res = await readAll(obs)
+ * expect(res).toEqual([1, 2, 3, 4]);
+ * ```
+ */
 export function readAll<T>(o: Observable<T>): Promise<T[]> {
   return toPromise.call(toArray.call(o));
 }
 
+/**
+ * @whatItDoes reads the first value from an observable and returns a promise
+ * with it. This should be used in combination with async/await.
+ *
+ * ## Example
+ *
+ * ```typescript
+ * const obs = of(1, 2, 3, 4);
+ * const res = await readFirst(obs)
+ * expect(res).toEqual(1);
+ * ```
+ */
 export function readFirst<T>(o: Observable<T>): Promise<T> {
   return toPromise.call(first.call(o));
 }