Added Nav Plugin tests

Summary:
Here I added two tests to test the persisted state reducer in the navigation pliugin.

I uncovered that my state reducer is not pure, as it calls the Date constructor, but I will fix this in a future update by passing the date recorded on the Android device when the nav event occurs and sending that via the socket connection.

For now I have modified the state reducer to take a date as part of the payload on a nav_event, or if none exists record the date as before. Also, if a page has no uri, but we want to record a nav event, I send null uri from the Android side. This doesn't send the uri as null to flipper; the uri object property simply doesn't exist. In this case I explicitly cast the undefined value for uri to null.

Reviewed By: jknoxville

Differential Revision: D16330958

fbshipit-source-id: fe338ea3a244df6ef33356bc7fdef8da9291dc68

src/plugins/navigation/index.js

@@ -14,12 +14,12 @@ type State = {||};
 type Data = {||};
 
 type NavigationEvent = {|
-  date: Date,
-  uri: ?String,
+  date: ?Date,
+  uri: ?string,
 |};
 
-type PersistedState = {|
-  navigationEvents: [NavigationEvent],
+export type PersistedState = {|
+  navigationEvents: Array<NavigationEvent>,
 |};
 
 export default class extends FlipperPlugin<State, {}, PersistedState> {
@@ -35,7 +35,7 @@ export default class extends FlipperPlugin<State, {}, PersistedState> {
   static persistedStateReducer = (
     persistedState: PersistedState,
     method: string,
-    payload: Object,
+    payload: NavigationEvent,
   ): $Shape<PersistedState> => {
     switch (method) {
       case 'nav_event':
@@ -43,7 +43,10 @@ export default class extends FlipperPlugin<State, {}, PersistedState> {
           ...persistedState,
           navigationEvents: [
             ...persistedState.navigationEvents,
-            {uri: payload.uri, date: new Date()},
+            {
+              uri: payload.uri === undefined ? null : payload.uri,
+              date: payload.date || new Date(),
+            },
           ],
         };
       default:
@@ -55,7 +58,7 @@ export default class extends FlipperPlugin<State, {}, PersistedState> {
 
   onKeyboardAction = (action: string) => {
     if (action === 'clear') {
-      this.props.setPersistedState({data: []});
+      this.props.setPersistedState({navigationEvents: []});
     }
   };