StateTransitionMachine.loadGraph reports success (#757)

Step one towards #586. This will enable us to chain runPagerank after
loadGraph only if the load went through successfully.

Test plan: Unit tests included.

src/app/credExplorer/state.js

@@ -79,7 +79,7 @@ export function initialState(): AppState {
 export interface StateTransitionMachineInterface {
   +setRepo: (Repo) => void;
   +setEdgeEvaluator: (EdgeEvaluator) => void;
-  +loadGraph: (Assets) => Promise<void>;
+  +loadGraph: (Assets) => Promise<boolean>;
   +runPagerank: (NodeAddressT) => Promise<void>;
 }
 /* In production, instantiate via createStateTransitionMachine; the constructor
@@ -167,7 +167,8 @@ export class StateTransitionMachine implements StateTransitionMachineInterface {
     }
   }
 
-  async loadGraph(assets: Assets) {
+  /** Loads the graph, reports whether it was successful */
+  async loadGraph(assets: Assets): Promise<boolean> {
     const state = this.getState();
     if (
       state.type !== "INITIALIZED" ||
@@ -182,6 +183,7 @@ export class StateTransitionMachine implements StateTransitionMachineInterface {
     };
     this.setState(loadingState);
     let newState: ?AppState;
+    let success = true;
     try {
       const graphWithAdapters = await this.loadGraphWithAdapters(assets, repo);
       newState = {
@@ -195,10 +197,13 @@ export class StateTransitionMachine implements StateTransitionMachineInterface {
     } catch (e) {
       console.error(e);
       newState = {...state, substate: {...substate, loading: "FAILED"}};
+      success = false;
     }
     if (deepEqual(this.getState(), loadingState)) {
       this.setState(newState);
+      return success;
     }
+    return false;
   }
 
   async runPagerank(totalScoreNodePrefix: NodeAddressT) {

src/app/credExplorer/state.test.js

@@ -226,7 +226,8 @@ describe("app/credExplorer/state", () => {
       const {getState, stm, loadGraphMock} = example(readyToLoadGraph());
       const gwa = graphWithAdapters();
       loadGraphMock.mockResolvedValue(gwa);
-      await stm.loadGraph(new Assets("/my/gateway/"));
+      const succeeded = await stm.loadGraph(new Assets("/my/gateway/"));
+      expect(succeeded).toBe(true);
       const state = getState();
       const substate = getSubstate(state);
       expect(loading(state)).toBe("NOT_LOADING");
@@ -246,7 +247,8 @@ describe("app/credExplorer/state", () => {
             resolve(graphWithAdapters());
           })
       );
-      await stm.loadGraph(new Assets("/my/gateway/"));
+      const succeeded = await stm.loadGraph(new Assets("/my/gateway/"));
+      expect(succeeded).toBe(false);
       const state = getState();
       const substate = getSubstate(state);
       expect(loading(state)).toBe("NOT_LOADING");
@@ -259,7 +261,8 @@ describe("app/credExplorer/state", () => {
       // $ExpectFlowError
       console.error = jest.fn();
       loadGraphMock.mockRejectedValue(error);
-      await stm.loadGraph(new Assets("/my/gateway/"));
+      const succeeded = await stm.loadGraph(new Assets("/my/gateway/"));
+      expect(succeeded).toBe(false);
       const state = getState();
       const substate = getSubstate(state);
       expect(loading(state)).toBe("FAILED");